Fluorescent substance, fluorescent composition, fluorescent mark carrier and optical reader therefor

ABSTRACT

A mark to be detected containing a fluorescent substance capable of emitting light of a wavelength different from that of an exciting light, containing: 
     a data area formed with a pattern corresponding to data to be recorded; and 
     a lead-in area formed at a site that is scanned prior to irradiation with the exciting light upon the data area, the lead-in area continuing a sufficient length greater than the longest continuous portion of the pattern formed at the data area, and the lead-in area that is formed at the site containing a fluorescent substance.

This application is a divisional of Application No. 08/553,667, filed onNov. 17, 1995, now U.S. Pat. No. 5,932,139. Application Ser. No.08/553,667 is the national phase of PCT International Application No.PCT/JP95/00463 filed on Mar. 17, 1995 under 35 U.S.C. §371. The entirecontents of each of the above identified applications are herebyincorporated by reference.

FIELD OF TECHNOLOGY

The present invention relates to a fluorescent substance excellent inlight emission, a method of preparing the fluorescent substance, afluorescent composition such as, for example, an inking medium for usein an ink jet printer, containing the fluorescent substance, afluorescent mark carrier such as, for example, postal envelopes, postalcards or postal parcels having a fluorescent mark formed by printing thefluorescent composition, and an optical reader and an optical readingsystem both operable to optically read the fluorescent mark at a highspeed.

BACKGROUND ART

(Prior Art 1)

In various fields of industries including the distribution industry, barcodes are widely utilized to control the physical distribution ofcommodities. The bar codes are also utilized having been printed onvarious cards such as, for example, pre-paid cards, commutation cardsand data cards. These bar codes are read by an optical reader such as,for example, an optical scanner which subsequently processes informationrepresented by the bar codes. Most bar codes carried by surfaces ofcommodities or cards are in the form of a pattern of stripes printed bythe use of a black inking medium against a white background and visibleto human eyes under visible rays of light. This visible mark is printeddirectly on merchandise or printed on a shaped sheet-like carrier whichis in turn affixed to merchandise.

On the other hand, attempts have been made to form a mark such as a barcode by the use of a fluorescent substance capable of emitting aninfrared region of light so that the fluorescent mark can be identifiedby an optical reader. While the fluorescent mark is generally invisibleto the human eyes, the fluorescent mark emits a fluorescent light whenthe fluorescent substance contained therein is excited upon irradiationof an external light of a particular wavelength and, therefore, byanalyzing the fluorescent light with an optical reader, informationrepresented by the fluorescent mark can be decoded or identified. Eventhe fluorescent mark is, as is the case with the visible mark, printeddirectly on merchandise or printed on a shaped sheet-like carrier whichis in turn affixed to merchandise.

As compared with the system in which change in intensity of lightreflected from the visible mark is read in handling merchandise, asystem for handling merchandise, including an optical reader for readingthe fluorescent mark, has numerous advantages, some of which are listedbelow.

(1) Reading of the fluorescent mark is seldom affected adversely by thecolor of the merchandise and, therefore, the reliability in reading thefluorescent mark is high with the reading error minimized.

(2) Even though the surface on which the fluorescent mark is formedbecomes dirty, infrared rays of light emitted from the fluorescent markhas such a long wavelength that the reading error would seldom occur andthe reliability is therefore high.

(3) Since the fluorescent substance is substantially colorless undervisible rays of light, printing of the fluorescent mark on themerchandise will bring no adverse effect on the aesthetic appearance ofthe merchandise.

(4) Since the fluorescent substance is so invisible under visible raysof light that no one can recognize the presence of the fluorescentsubstance, it can provide security of information.

Particulars of interest in this connection are disclosed in, forexample, the Japanese Patent Publications No. 55-33837, No. 60-29996 andNo. 62-24024.

(Prior Art 2)

The fluorescent mark discussed above is formed by printing a fluorescentinking medium containing a fluorescent substance on a carrier such as,for example, a surface of the merchandise in a predetermined pattern. Aninfrared fluorescent inking medium has long been known and is disclosedin, for example, the U.S. Pat. No. 4,202,491. The infrared fluorescentinking medium disclosed therein is prepared from an inorganicfluorescent substance containing one or a mixture of neodymium (Nd),ytterbium (Yb) and erbium (Er). The inorganic fluorescent substancewhich utilizes Nd as an optically active element is known to emit afluorescent light having a maximum intensity at about 1,050 nm inwavelength when irradiated with an exciting light of 800 nm emitted by aGaAlAs light emitting diode. The inorganic fluorescent substancecontaining a mixture of Nb and Yb as an optically active element isknown to emit a fluorescent light having a maximum intensity at about980 nm in wavelength when irradiated with an exciting light of 800 nmemitted by a GaAlAs light emitting diode. Similarly, the inorganicfluorescent substance containing a mixture of Yb and Er as an opticallyactive element is known to emit a fluorescent light having a maximumintensity at about 1,050 nm in wavelength when irradiated with anexciting light of 940 nm emitted by a GaAs light emitting diode, and theinorganic fluorescent substance containing a mixture of Nd, Yb and Er asan optically active element is known to emit a fluorescent light havinga maximum intensity at about 1,050 nm in wavelength when irradiated withan exciting light of 800 nm emitted by a GaAlAs light emitting diode.

(Prior Art 3)

The fluorescent substance disclosed in, for example, the Japanese PatentPublication No. 56-4598 makes use as the optically active element of Ndhaving a high absorption characteristic with respect to the infraredregion of light, in combination with a fluorescent material capable ofexhibiting a high intensity of light emission such as, for example, analkaline metal salt (for example, Na₂MoO₄ or the like) which is materialfor the matrix having a high efficiency of transmission of excitingenergies from the optically active element to the emission center, or Ybhaving an emission center capable of favorably matching in wavelengthwith a Si photodetector.

(Prior Art 4)

For example, the Japanese Patent Publications No. 54-22326 and No.61-18231 disclose a method of detecting the presence or absence of thefluorescent mark. In this known method, the fluorescent mark is preparedby the use of a fluorescent substance which emits a fluorescent lightwhen irradiated with an exciting light within the infrared region ofwavelength. This known method utilizes the difference between the centerwavelength of the exciting light projected onto the fluorescent mark andthat of the fluorescent light emitted from the fluorescent substance asa result of the irradiation of the exciting light and, for this purpose,only the fluorescent light is separated by an optical filter from raysof light reflected from the fluorescent mark so that the presence orabsence of the fluorescent mark can be eventually detected.

The applicant has suggested a method of and an apparatus for detectingthe position of a fluorescent mark by intermittently irradiating thefluorescent marking with the exciting light and then detecting thepresence or absence of afterglow emitted from the fluorescent markingduring the intermission of irradiation of the exciting light. (See, forexample, the Japanese Laid-open Patent Publication No. 5-20512.)

(Prior Art 5)

FIG. 70 illustrates the prior art optical reading apparatus. Thefluorescent mark shown therein is in the form of a fluorescent bar code401 comprised of a pattern of parallel bars formed by printing thefluorescent inking medium on a sheet-like carrier 404 such as, forexample, a label. The fluorescent inking medium used to form the barcode 401 contains fluorescent microparticles dispersed and retained in abinder, said fluorescent microparticles being of a kind which emit, whenexcited by an exciting light of a particular wavelength, for example,infrared rays of light 402, a fluorescent light 403 of a wavelengthdifferent from that of the infrared rays of light 402.

An optical reading apparatus for reading information from thefluorescent bar code 401 includes a light emitter 405 for emitting theinfrared rays of light 402, a light receiver 407 for detecting thefluorescent light 403 from the bar code 401 and rays of light 406reflected from the carrier 404 and for converting them into an electricsignal, an amplifier 408 for amplifying the electric signal and foroutputting an analog reproduction signal, and a signal detector 409 fordetecting from the analog reproduction signal of the amplifier 408information represented by the bar code 401. The signal detector 409used therein includes an analog-to-digital (A/D) converter which isoperable to digitize the analog reproduction signal so that theinformation represented by the fluorescent bar code 401 can bereproduced.

For digitization of the analog reproduction signal, a comparator isgenerally utilized, having an input stage which is adapted to receivethe analog reproduction signal A and a slice signal B of a predeterminedlevel shown in FIG. 66 so that the analog reproduction signal A can besliced by the slice signal B to provide a digitized signal.

(Problem 1)

In the various fluorescent substances and the various fluorescent marksformed by printing the fluorescent inking media containing therespective fluorescent substances, both having hitherto been suggested,neither the relationship between the particle size of the particularfluorescent substance and the wavelength of the exciting light used northe relationship between the particle size of the particular fluorescentsubstance and the wavelength of the fluorescent light emitted by suchparticular fluorescent substance has been taken into consideration. Theconventional fluorescent substance has a particle size as relativelylarge as 5 to 6 μm. On the other hand, for a light source for excitingthe fluorescent substance, a semiconductor laser, for example, isgenerally utilized, capable of emitting a laser beam of about 0.8 μm inwavelength while the fluorescent light emitted from the conventionalfluorescent substance has a wavelength of about 1 μm.

As discussed above, the conventional fluorescent particles have arelatively great particle size, i.e., a particle size as great as about5 to 7.5 times the wavelength of any one of the exciting light and thefluorescent light. For this reason, if the fluorescent mar is preparedby the use of the fluorescent inking medium containing the fluorescentparticles of that particle size, the fluorescent particles are depositedin such an overlapping relation that the exciting light projectedtowards a deposit of the fluorescent inking medium will not reach someof the fluorescent particles at a deep region of the deposit of thefluorescent inking medium, and for this reason, the efficiency ofactivation (excitation) of the fluorescent substance is lowered.

Even if some of the fluorescent particles at the deep region of thedeposit of the fluorescent inking medium are excited to emit afluorescent light, the fluorescent light so emitted tends to be partlyintercepted by other fluorescent particles residing over such some ofthe fluorescent particles within the deposit of the inking medium, withthe intensity of the fluorescent light consequently lowered.Consequently, the fluorescent light of such a low intensity oftencreates a problem associated with the reliability in detecting thepresence or absence of the fluorescent mark.

Thus, partly because the efficiency of activation (excitation) of thefluorescent substance is low and partly because part of the fluorescentlight excited will not emerges outwardly from an exterior surface of thedeposit of the fluorescent inking medium and, hence, the intensity ofthe fluorescent light is consequently low, the prior art fluorescentsubstance poses a problem associated with the reliability in detectingthe presence or absence of the fluorescent mark.

(Problem 2)

The fluorescent substance generally has such a property that whenirradiated with the exciting light the fluorescent substance isactivated to emit a fluorescent light in a progressively increasingquantity, but in the absence of the exciting light the quantity of thefluorescent light emitted decreases progressively. With the conventionalfluorescent substance, the length of time, that is, the rise time, whichpasses from the start of irradiation of the exciting light upon thefluorescent substance and until the resultant fluorescent light attainsa desired intensity is long. For this reason, a high velocity ofmovement of the fluorescent mark carrier relative to the optical readercannot be employed, constituting an obstruction to the use of a highspeed optical reader. If the relative velocity is increased, informationrepresented by the fluorescent mark will no longer be read accuratelyand properly.

Although this is related to the relatively long rise time of thefluorescent light referred to above, the conventional fluorescentsubstance has a length of time (that is, the fall time) which passesfrom the interruption of irradiation of the exciting light upon thefluorescent substance and until the intensity of the fluorescentafterglow attains zero, that is, until the fluorescent light is nolonger detected is long as well. For this reason, where the fluorescentmark consists of a plurality of parallel fluorescent bars, reduction inspacing between each neighboring fluorescent bars will render the lightreceiving element to detect a fluorescent afterglow emanating from theadjoining fluorescent bar, failing to provide an accurate informationreading.

(Problem 3)

Inorganic powdery fluorescent pigments such as Nd, Yb and Er discussedhereinbefore have a relatively large particle size. Although thisparticle size would pose no problem if the fluorescent particles aretramped down with resin before use, the use of the fluorescent pigmentof a relatively large particle size in an inking medium for use with anink jet printer would, unless the particle size is reduced, resultneither in a homogenous and beautiful print, nor in a high resolutionduring information reading. On the other hand, if the fluorescentparticles are finely pulverized with the use of a mill, the fluorescentoutput would eventually decrease considerably.

The inventors of the present invention have also found that, in additionto the above discussed problems, the inorganic fluorescent pigmentsbring about an additional problem in that the response of thefluorescent substance to emit the fluorescent light subsequent toreceipt of the exciting light is so low that a high speed reading isdifficult to achieve.

(Problem 4)

In the Japanese Patent Publication No. 56-4598 referred to above, thereis disclosed that the matrix material of the infrared-excitablefluorescent substance contains alkaline metal cations, Li⁺Na⁺, if ananion thereof is chosen MoO₂ ²⁻ or Wo₄ ²⁻. Since a salt of alkalinemetal which is generally a monovalent metal has a relatively weak bondbetween the anion and the cation because of a small valence sufficientto be easily released to form a hydrate, the alkaline metal salt iswater-soluble. Accordingly, the fluorescent substance prepared from thealkaline metal salt as a matrix material is extremely poor in waterresistance to such an extent as to result in an obnoxious problem inpractical use.

The infrared-excitable fluorescent substance is prepared by weighing,mixing and pressure-forming only the starting materials (for example,Na₂CO₃, MoO₃, Nd₂O₃ and Yb₂O₃), incinerating the preformed mixture andsubsequently mechanically pulverizing it to provide the powderyfluorescent substance. In such case, the resultant fluorescent particleshave a minimum particle size as small as about 5 μm. Although thisparticle size permits the fluorescent particles to be used as a materialfor a printing ink medium such as used in, for example, a screenprinting technique, the fluorescent particles of this particle sizecannot be used as a material for an inking medium for use with an inkjet printer or for use in an inked ribbon. This is because the inkingmedium for use in the practice of a printing technique requires thefluorescent substance of 1 μm or smaller in particle size, thefluorescent substance of about 5 μm in particle size is not suited as amaterial for the inking medium that is used with the ink jet printer orin the inked ribbon.

The Japanese Laid-open Patent Publication No. 5-261634 referred to abovediscloses that the fluorescent substance having its matrix material inthe form of a salt of PO₄ and activated by Nd and Yb can be used in aninking medium for use in an offset printing technique provided that suchfluorescent substance is pulverized to a particle size within the rangeof 0.1 to 3 μm.

However, the infrared-excitable fluorescent substance of this system hasbeen found that both of the rise time, required for it to emit afluorescent light of the maximum intensity subsequent to irradiation ofinfrared rays of light, and the fall time required for the intensity ofthe fluorescent light to attain zero subsequent to interruption of theinfrared irradiation are extremely long, and therefore, it cannotsatisfactorily be used where the exciting light is in the form of apulsating light of short duration and/or where a high speed readingwith, for example, a high speed scanner is desired.

The inventors of the present invention, in an attempt to develop aninfrared-excitable fluorescent substance having a high response, haveexamined the use of Na₂MoO₄ as a matrix of the infrared-excitablefluorescent substance, but have found that, because Na₂MoO₄ iswater-soluble, the fluorescent substance having its matrix added withoptically active elements has exhibited a poor water resistance. Also,the fluorescent substance obtained had a particle size greater than afew microns and have therefore been found not suited for use as amaterial for the ink jet printer or the inked ribbon or in a printingtechnique such as an offset printing process.

(Problem 5)

Hitherto, in preparing a fluorescent composition such as, for example,the inking medium for use with an ink jet printer and containingfluorescent particles, none of the particle size of the fluorescentsubstance used, the density of the fluorescent substance and/or thedensity of a binder used, and the relationship among viscosity, surfacetension, specific resistance and pH value has not taken intoconsideration. For this reason, the fluorescent particles contained inthe fluorescent composition have such problems that the fluorescentparticles are apt to sediment in the fluorescent composition, exhibitingan unsatisfactory dispersion stability, that the fluorescent compositiontends to run during the printing and/or that the fluorescent output islow.

(Problem 6)

In the prior art fluorescent inking medium containing the fluorescentparticles, the fluorescent substance is employed in a quantity generallywithin the range of 30 to 85 wt % relative to the total weight of theinking medium and is in the form of an inorganic compound having arelatively large particle size as discussed hereinabove. The use of thefluorescent substance in such a large quantity brings about such aproblem that a fluorescent ink deposit formed by printing thefluorescent inking medium is so raised as to provide a visibleindication of the presence of the ink deposit. This is problematic interms of security particularly when a fluorescent mark is desired to beformed by depositing the inking medium at a location where the inkdeposit will not constitute any obstruction to the eyes.

(Problem 7)

With respect to the fluorescent ink deposit formed by the use of theconventional fluorescent inking medium containing the fluorescentparticles, no surface roughness of the ink deposit has been studied.Since the fluorescent substance of the relatively large particle size asdiscussed above has been employed, the surface of the ink deposit isrelatively rough, having minute surface irregularities. Irradiation ofthe exciting light upon the rough-surfaced ink deposit tends to resultin scattering of the exciting light upon the surface of the ink deposit,accompanying reduction in quantity of the exciting light penetratinginto the fluorescent ink deposit. Also, with the rough-surfaced inkdeposit, the fluorescent light emitted internally from the fluorescentink deposit is apt to scatter in all directions at the surface of theink deposit and, therefore, the quantity of the fluorescent lightreceived by a light receiving element may be reduced correspondingly.

Once the above discussed phenomenon occurs, an output generated from thelight receiving element in response to detection of the fluorescentlight emitted from the fluorescent ink deposit is so low as to bringabout a problem associated with the reliability in detecting thepresence or absence of the fluorescent mark.

(Problem 8)

An optical reading apparatus used in connection with the fluorescentmark is known and includes a semitransparent mirror disposed generallyintermediate between the fluorescent mark to be detected and aphotoelectric detector assembly inclusive of light emitting andreceiving elements. The known optical reading apparatus is so structuredthat the exciting light emitted from the light emitting element may beprojected through the semitransparent mirror onto the fluorescent markcarrier so that the fluorescent light emitted from the fluorescent markon the carrier can pass through the same semitransparent mirror beforeit is detected by the light receiving element. With this structure, ithas been observed that as the exciting light travels through thesemitransparent mirror, generally half of the exciting light may bereflected in directions other than the direction towards the fluorescentmark carrier and/or that as the fluorescent light emitted from thefluorescent mark on the carrier travels through the semitransparentmirror, generally half o the fluorescent light may be reflected indirections other than the direction towards the light receiving element.For this reason, the quantity of the exciting light necessary toactivate the fluorescent substance is in practice small and, hence, thequantity of the fluorescent light emitted is correspondingly small and,yet, the light receiving element receives the fluorescent light in aquantity generally half of the actually emitted fluorescent light.Therefore, the light receiving element issues a considerably low output,so low as to bring about a problem associated with the reliability indetecting the fluorescent mark.

(Problem 9)

In the prior art optical reading apparatus, the exciting light emittedfrom the light emitting element forms a round irradiating pattern of asize sufficient to encompass the size of the bar code forming thefluorescent mark. Irradiation of the round light spot upon thefluorescent mark does not affords a sufficient area of surface to beilluminated and the intensity of the fluorescent light emitted from thefluorescent mark is consequently low. If an attempt is made to increasethe size of the round light spot to thereby increase the area of surfaceto be illuminated, the exciting light will encompass not only the barcode of interest, but also the bar code adjoining such bar code ofinterest. This in turn brings about reduction in S/N (signal-to-noise)ratio, accompanying a problem associated with the reliability indetecting the fluorescent mark.

(Problem 10)

In designing the prior art optical reading apparatus, neither the risetime of the fluorescent light subsequent to irradiation of the excitinglight, nor the relationship between the width of a slit extending in adirection of transport of the fluorescent mark carrier and the speed oftransport of the fluorescent mark carrier is taken into consideration.

Also, neither the fall time of the fluorescent light subsequent tointerruption of the exciting light, nor the relationship between theinterval between the neighboring bars of the fluorescent mark (i.e., thefluorescent bar code) and the speed of transport of the fluorescent markcarrier is taken into consideration.

Because of the foregoing, no information represented by the fluorescentink deposit on the fluorescent mark carrier can be read.

(Problem 11)

In the prior art optical reading apparatus, a slit member is interposedbetween the sheet-like fluorescent mark carrier such as, for example, apaper, and an object lens assembly so that only that portion of thefluorescent light emitted from the fluorescent mark which is desired tobe detected is received by the light receiving element through the slitin the slit member. Although this will bring about no problem if thefluorescent mark carrier has a substantially uniform thickness, there isa problem in that, if the fluorescent mark carrier having a relativelygreat, but irregular thickness is transported, the fluorescent markcarrier being transported may be blocked with its front engaged with theslit and/or the slit will be damaged.

(Problem 12)

The prior art method of detecting the mark such as disclosed in theJapanese Patent Publications No. 54-22326 and No. 61-18231 and theJapanese Laid-open Patent Publications No. 3-16369 and No. 5-20512 allreferred to above, is such that the fluorescent light emitted from thefluorescent mark as a result of excitation by the exciting light isdetected by a detector. However, the quantity of the fluorescent lightincident on the detector considerably varied with change in environmentsand conditions in and under which the detection is performed and,therefore, in order to secure a high accuracy of detection, acomplicated circuit processing is required, or the condition of use islimited.

As a result of studies conducted by the inventors of the presentinvention in view of the foregoing problems, it has been found that anyone of the prior art detecting method is unable to properly andaccurately monitor the change in detecting condition because of aninsufficient quantity of information available other than dataassociated with the fluorescent mark.

(Problem 13)

In another prior art method in which an optical filter used to separatethe exciting light, which has been reflected, and the fluorescent lightfrom each other, since the wavelength of the emission center of thereflected exciting light and that of the fluorescent light are close toeach other and the intensity of the fluorescent light is extremely lowas compared with that of the reflected exciting light, the both cannotbe properly separated from each other with no difficulty and, in acertain case, most of the reflected exciting light may remainunseparated and enter the light receiving element together with thefluorescent light. Once this occurs, the accuracy of detection islowered.

(Problem 14)

According to the fluorescent mark detecting method disclosed in, forexample, the Japanese Laid-open Patent Publications No. 3-16369 and No.5-20512 referred to above, if external rays of light of a wavelengthmatching with or in the vicinity of the wavelength of the fluorescentlight exist in the environment in which the fluorescent light is beingdetected, such rays of light may be sensed by and converted into anelectric output by the light receiving element. This leads to generationof false information that, even though no fluorescent light has yet beenemitted, the fluorescent light was detected. In order to avoid suchfalse information, both of the site of emission of the exciting lightand the site of detection of the fluorescent light are required to beshielded from the external light, thus limiting the environment in whichthe system is used.

(Problem 15)

In the optical reading apparatus of a structure shown in FIG. 71, bothof the level and the amplitude of the analog reproduction signaldiscussed hereinbefore are considerably affected by physical surfaceproperties of the carrier on which the bar code is formed in the form ofthe fluorescent mark. More specifically, where the surface of thecarrier is made of material having a propensity of absorbing atransparent inking medium and also the exciting light projected from anilluminator unit, the quantity of the fluorescent light emitted from thefluorescent bar code and the quantity of light reflected from thecarrier are so small that, as shown in FIG. 71(b), the analogreproduction signal exhibits a low level and a low amplitude.

Also, where the carrier is made of material having a propensity ofabsorbing the transparent inking medium and also that of reflecting thelight projected by the illuminator unit, the analog reproduction signalis apt to offset towards a high level as shown in FIG. 71(c). Moreover,where the carrier is made of material having a propensity of absorbinglittle transparent inking medium, but absorbing the light projected bythe illuminator unit, the analog reproduction signal exhibits anincreased amplitude as shown in FIG. 71(a).

Accordingly, with the prior art reading apparatus in which variation inwaveform of the analog reproduction signal resulting from difference intype of the carriers on which the fluorescent bar codes are formed istaken into consideration, when the single reading apparatus is used toread one at a time the fluorescent bar codes formed on, for example, therespective carriers made of different materials, or when the readingapparatus is used to read one at a time the fluorescent bar codes formedon different portions of the single carrier which are made of varyingmaterials, a problem is apt to occur in that the bar codes will not beaccurately read. This problem may be avoided if an optical filter (asingle wavelength filter) operable to cut off the entire light reflectedfrom the carrier is disposed in front of the light receiving element.However, the single wavelength filter is expensive and cannot, in termsof cost, be installed in the optical reading apparatus and, instead, theabove discussed problem does often occur since a band-pass filteroperable to cut off a portion of the reflected light is generallyemployed.

Accordingly, a primary object of the present invention is to provide ahighly reliable fluorescent substance having a high emissive output, afluorescent composition, a fluorescent mark carrier, an optical readingapparatus, a merchandise sorting apparatus and a merchandise sortingsystem all of which are effective to substantially eliminate the abovediscussed problems inherent in the prior art.

Another important object of the present invention is to provide thefluorescent substance and the fluorescent composition which areeffective to substantially eliminate the above discussed problemsinherent in the prior art, excellent in durability, fine in particlesize suitable for use in various printing techniques such as thoseemploying an ink jet printer or an inked ribbon, and capable ofexhibiting a high response.

A further important object of the present invention is to provide anoptically detectable mark effective to substantially eliminate the abovediscussed problems inherent in the prior art and with which change inenvironmental conditions in which data are being detected can be readilyand properly determined.

A still further important object of the present invention is to providea detecting method and an optical reading apparatus effective tosubstantially eliminate the above discussed problems inherent in theprior art and capable of accomplishing accurate detection of theposition at which the mark is formed, regardless of deterioration incondition in which the fluorescent light emitted from the mark isdetected.

A yet further important object of the present invention is to providethe optical reading apparatus effective to substantially eliminate theabove discussed problems inherent in the prior art and capable ofaccomplishing assured detection of the fluorescent mark without beingadversely affected by environments in which it is used.

A different important object of the present invention is to provide thereading apparatus effective to substantially eliminate the abovediscussed problems inherent in the prior art and capable of accuratelyreading the fluorescent light at all times with no need to use theexpensive single wavelength filter and regardless of the waveform of theanalog reproduction signal.

DISCLOSURE OF THE INVENTION

The first invention is directed to the fluorescent substance of a kindcapable of emitting, in response to irradiation of the exciting light, afluorescent light of a wavelength different from that of the excitinglight and is characterized in that, in order to accomplish the foregoingobjects, the average particle size of the fluorescent substance being ofsuper microparticles is smaller than the maximum intensity of thefluorescent light emitted by such fluorescent substance.

The second invention is directed to the fluorescent substance of a kindcapable of emitting, in response to irradiation of the exciting light, afluorescent light of a wavelength different from that of the excitinglight and is characterized in that, in order to accomplish the foregoingobjects, the average particle size of the fluorescent substance being ofultra-microparticles is smaller than the maximum intensity of theexciting light.

The fluorescent substance according to the third invention ischaracterized in that, in order to accomplish the foregoing objects, itcomprises a salt of oxyacid containing at least one optical activeelement selected from the group consisting of Nd, Yb and Er, said saltof oxyacid being expressed by, for example, the following generalformula (1) or (2):

Ln_(X)A_(1−X)PO₄  (1)

wherein:

Ln represents at least one element selected from the group consisting ofNd, Yb and Er;

A represents at least one element selected from the group consisting ofY, La, Gd, Bi, Ce, Lu, In and Tb; and

X represents a value within the range of 0.01 to 0.99.

 DE_(1−X)Ln_(X)P_(Y)O_(Z)  (2)

 wherein:

D represents at least one element selected from the group consisting ofLi, Na, K, Rb and Cs;

E represents at least one element selected from the group consisting ofY, La, Gd, Bi, Ce, Lu, In and Tb;

Ln represents at least one element selected from the group consisting ofNd, Yb and Er;

X represents a value within the range of 0.01 to 0.99;

Y represents a value within the range of 1 to 5; and

Z represents a value within the range of 4 to 14.

The fluorescent substance according to the fourth invention ischaracterized in that, in order to accomplish the foregoing objects, itcomprises Fe and Er, both as an optical active element, and, other thanthese optical active elements, at least one element selected from thegroup consisting of Sc, Ga, Al, In, Y, Bi, Ce, Gd, Lu and La and isexpressed by one of the following general formulas (3), (4) and (5):

G₃J₅O₁₂  (3)

GJO₃  (4)

G₂J₄O₁₂  (5)

wherein:

G represents at least one element selected from the group consisting ofY, Bi, Ce, Gd, Lu and La, and Er; and

J represents at least one element selected from the group consisting ofSc, Ga, Al and In, and Fe.

The fluorescent substance according to the fifth invention ischaracterized in that, in order to accomplish the foregoing objects, itcomprises Yb as an optical active element and, other than that opticalactive element, at least one element selected from the group consistingof Sc, Ga, Al, In, Y, Bi, Ce, Gd, Lu and La and is expressed by one ofthe following general formulas (6), (7) and (8):

L₃M₅O₁₂  (6)

LMO₃  (7)

L_(2 M) ₄O₁₂  (8)

wherein:

L represents at least one element selected from the group consisting ofY, Bi, Ce, Gd, Lu and La, and Yb; and

M represents at least one element selected from the group consisting ofSc, Ga, Al and In.

The fluorescent substance according to the sixth invention ischaracterized in that, in order to accomplish the foregoing objects, itcomprises at least one organic substance containing rare earth element,said organic substance being selected from the group consisting of Nb,Yb and Er and carried with an organic substance such as, for example,polymethine, anthraquinone, dithiol metal, phthalocyanine, indophenol orazo dyestuff of a kind having an absorption band within the infraredregion of rays of light.

The seventh invention is characterized in that, in order to accomplishthe foregoing objects, it contains at least one of Nb and Yb as anoptical active element and, other than this optical active element, atleast one oxide of Mo or W and an alkaline earth metal and is expressedby one of the following general formulas (9) and (10):

(Nd_(1−X)Yb_(X))_(Y)Q_(Z)(RO₄)  (9)

wherein:

Q represents at least one element selected from the group consisting ofCa, Mg, Sr and Ba;

R represents at least one element selected from the group Mo and W;

X represents a value within the range of 0 to 1;

Y represents a value greater than 0, but smaller than 1; and

Z represents a value greater than 0, but smaller than 1.

(Nd_(1−X)Yb_(X))_(2Y)Q_(8−3Y)(RO₄)₈  (10)

wherein:

Q represents at least one element selected from the group consisting ofCa, Mg, Sr and Ba;

R represents at least one element selected from the group Mo and W;

X represents a value within the range of 0 to 1; and

Y represents a value greater than 0, but equal to or smaller than 8/3.

A method of preparing the fluorescent substance according to the eighthinvention is characterized in that, in order to accomplish the foregoingobjects, at least one optical active element selected from the groupconsisting of Nd and Yb, at least one oxide of one of Mo and W and analkaline earth metal are added to a flux material containing a saltexpressed by T₂RO₄.nH₂O (wherein T is at least one element selected fromthe group consisting of Li, Na and K, R is at least one element selectedfrom the group consisting of Mo and W, and n is a value greater than 0)which is subsequently calcinated, followed by dissolution of theincinerated product with the use of a solvent to remove the fluxmaterial.

The fluorescent composition according to the ninth invention ischaracterized in that, in order to accomplish the foregoing objects, itcomprises a fluorescent substance in the form of ultra-microparticlescapable of emitting a fluorescent light of a wavelength different fromthat of the exciting light and having an average particle size smallerthan the wavelength of the maximum intensity of the fluorescent light, abinder transparent to both of the exciting light and the fluorescentlight, and a solvent.

The fluorescent composition according to the tenth invention ischaracterized in that, in order to accomplish the foregoing objects, itcomprises a fluorescent substance in the form of ultra-microparticlescapable of emitting a fluorescent light of a wavelength different fromthat of the exciting light and having an average particle size smallerthan the wavelength of the maximum intensity of the exciting light, abinder transparent to both of the exciting light and the fluorescentlight, and a solvent.

The fluorescent composition according to the eleventh invention ischaracterized in that, in order to accomplish the foregoing objects, itcomprises a fluorescent substance containing at least one organicsubstance which contains a rare earth element and which is selected fromthe group consisting of Nb, Yb and Er carried with an organic substancehaving an absorption band within the infrared region of light, and anorganic binder.

The fluorescent composition according to the twelfth invention ischaracterized in that, in order to accomplish the foregoing objects, itcomprises a fluorescent substance containing at least one of Nb and Ybas an optical active element and, other than this optical activeelement, at least one oxide of one of Mo and W and an alkaline earthmetal, and an organic binder.

The inked ribbon according to the thirteenth invention is characterizedin that, in order to accomplish the foregoing object, it comprises atape-like carrier deposited with the fluorescent composition comprisinga fluorescent substance containing at least one of Nb and Yb as anoptical active element and, other than this optical active element, atleast one oxide of one of Mo and W and an alkaline earth metal, whichfluorescent substance is dispersed and retained in an organic binder.

The fluorescent mark carrier according to the fourteenth invention ischaracterized in that, in order to accomplish the foregoing objects, thefluorescent mark containing the fluorescent substance in the form ofultra-microparticles capable of emitting a fluorescent light of awavelength different from that of the exciting light and having anaverage particle size smaller than the wavelength of the maximumintensity of the fluorescent light is printed thereon.

The fluorescent mark carrier according to the fifteenth invention ischaracterized in that, in order to accomplish the foregoing objects, thefluorescent mark containing the fluorescent substance in the form ofultra-microparticles capable of emitting a fluorescent light of awavelength different from that of the exciting light and having anaverage particle size smaller than the wavelength of the maximumintensity of the exciting light is printed thereon.

In order to accomplish the foregoing objects, the sixteenth invention ischaracterized by a fluorescent mark carrier printed with a fluorescentmark containing fluorescent particles capable of emitting a fluorescentlight of a wavelength different from that of the exciting light, thecontent of said fluorescent particles in the fluorescent mark beinggreater than 1 wt %, but smaller than 30 wt %.

In order to accomplish the foregoing objects, the seventeenth inventionis characterized by the fluorescent mark carrier printed with afluorescent mark containing fluorescent particles capable of emitting afluorescent light of a wavelength different from that of the excitinglight, a deposit of the fluorescent inking medium having a thickness notgreater than 35 times the particle size of the fluorescent particles.

In order to accomplish the foregoing objects, the eighteenth inventionis characterized by the fluorescent mark carrier printed with afluorescent mark containing fluorescent particles capable of emitting afluorescent light of a wavelength different from that of the excitinglight and a binder, said binder having a light transmissivity withrespect to each of the exciting and fluorescent light being not lowerthan 80%.

In order to accomplish the foregoing objects, the fluorescent markcarrier according to the nineteenth invention is characterized in thatthe fluorescent particles capable of emitting a fluorescent light of awavelength different from that of the exciting light are deposited on anaggregation of fibers.

In order to accomplish the foregoing objects, the fluorescent markcarrier according to the twentieth invention is characterized in that afluorescent ink deposit containing the fluorescent substance capable ofemitting a fluorescent light of a wavelength different from that of theexciting light has a 20% or lower visible ray absorption characteristic.

In order to accomplish the foregoing objects, the twenty-first inventionis directed to an optical reading apparatus comprising a light emittingelement for irradiating with the exciting light a fluorescent markcarrier carrying a fluorescent mark containing the fluorescentsubstance, a mirror for reflecting light from the fluorescent substanceand a light receiving element for receiving the light reflected by themirror, which apparatus is characterized in that the mirror has aportion thereof provided with a light transmitting region such as, forexample, a perforation, for allowing a substantially entire quantity ofthe exciting light from the light emitting element to pass therethroughand is in the form of a total reflecting mirror such as, for example, afront surfaced mirror, having a reflectivity of higher than 50%.

In order to accomplish the foregoing objects, the twenty-secondinvention is directed to an optical reading apparatus comprising a lightemitting element for irradiating with the exciting light a fluorescentmark carrier carrying a bar code containing the fluorescent substance,and a light receiving element for receiving light from the fluorescentsubstance, which apparatus is characterized in that the exciting lightis projected in an irradiating pattern of a generally elliptical shapehaving its major axis extending in a direction lengthwise of the barcode.

In order to accomplish the foregoing objects, the twenty-third inventionis directed to an optical reading apparatus comprising a light emittingelement for irradiating with the exciting light a fluorescent markcarrier printed with the fluorescent substance, a light receivingelement for receiving a fluorescent light from the fluorescent markcarrier, a slit member disposed on an optical path between the lightemitting element and the light receiving element, and a transport meansfor transporting the fluorescent mark carrier in a predetermineddirection, which apparatus is characterized in that the transport meanstransports the fluorescent mark carrier at a velocity v which has thefollowing relationship:

d/v≧tu

wherein d represents the length of an opening in the slit member asmeasured in a direction conforming to the direction of transport of thefluorescent mark carrier, v represents the velocity of transport of thefluorescent mark carrier and tu represents the length of time from thetiming at which the fluorescent substance receives the exciting light tothe timing at which the intensity of the light emitted by thefluorescent substance attains 90% of the maximum possible intensitythereof.

In order to accomplish the foregoing objects, the twenty-fourthinvention is directed to an optical reading apparatus comprising a lightemitting element for irradiating with the exciting light a fluorescentmark carrier printed with the fluorescent substance, a light receivingelement for receiving a fluorescent light from the fluorescent markcarrier and a transport means for transporting the fluorescent markcarrier in a predetermined direction, which apparatus is characterizedin that the transport means transports the fluorescent mark carrier at avelocity v which has the following relationship:

L/v≧td

wherein L represents the interval between neighboring portions printedwith the fluorescent substance with respect to the direction oftransport, v represents the velocity of transport of the fluorescentmark carrier, and td represents the length of time from the timing atwhich irradiation of the exciting light is interrupted to the timing atwhich the fluorescent afterglow attenuates by a quantity correspondingto 80% of the maximum possible intensity thereof.

In order to accomplish the foregoing objects, the twenty-fifth inventionprovides an optical reading apparatus comprising a light emittingelement for irradiating with the exciting light a fluorescent markcarrier carrying the fluorescent substance, a light receiving elementfor receiving a fluorescent light from the fluorescent mark carrier, atransport means for transporting the fluorescent mark carrier in apredetermined direction, a first convex lens disposed on an optical pathfrom the fluorescent mark carrier to the light receiving element andhaving a flat surface oriented towards the fluorescent mark carrier, asecond convex lens disposed on an optical path from the fluorescent markcarrier to the light receiving element and having a flat surfaceoriented towards the light receiving element, and a slit member disposedbetween the second convex lens and the light receiving element.

In order to accomplish the foregoing objects, the twenty-sixth inventionis directed to an optical reading apparatus comprising a light emittingelement for irradiating with the exciting light a fluorescent markcarrier printed with the fluorescent substance, and a light receivingelement for receiving a fluorescent light from the fluorescent markcarrier, characterized in that the light emitting element is asemiconductor laser diode, a drive circuit for driving the semiconductorlaser diode having an automatic power control function, and there isprovided a hold circuit for monitoring the exciting light emitted fromthe semiconductor laser diode and holding an output condition of theexciting light such that based on a signal from the hold circuit anoutput condition of the exciting light from the semiconductor laserdiode is controlled by the drive circuit.

In order to accomplish the foregoing objects, a merchandise sortingapparatus according to the twenty-seventh invention is characterized inthat the merchandise sorting apparatus comprises a light emittingelement for irradiating with the exciting light a fluorescent markcarrier printed with the fluorescent substance, a light emitting elementfor receiving a fluorescent light from the fluorescent mark carrier, aslit member disposed on an optical path between the light emittingelement and the light receiving element, a transport means fortransporting the fluorescent mark carrier in a predetermined direction,and a sorting means for sorting the fluorescent mark carrier, in thatthe length d of an opening in the slit member as measured in a directionconforming to the direction of transport of the fluorescent markcarrier, the velocity v of transport of the fluorescent mark carrier bythe transport means, and the length of time tu from the timing at whichthe fluorescent substance receives the exciting light to the timing atwhich the intensity of the light emitted by the fluorescent substanceattains 90% of the maximum possible intensity thereof have arelationship of (d/v≧tu), and in that information represented by afluorescent ink deposit provided on the fluorescent mark carrier is readby the exciting light and the fluorescent light passing through a slitformed in the slit member, said fluorescent mark carrier being sortedaccording to such information.

In order to accomplish the foregoing objects, a merchandise sortingapparatus according to the twenty-eighth invention is characterized inthat the merchandise sorting apparatus comprises a light emittingelement for irradiating with the exciting light a fluorescent markcarrier printed with the fluorescent substance, a light emitting elementfor receiving a fluorescent light from the fluorescent mark carrier, aslit member disposed on an optical path between the light emittingelement and the light receiving element, a transport means fortransporting the fluorescent mark carrier in a predetermined direction,and a sorting means for sorting the fluorescent mark carrier, in thatthe interval between neighboring portions printed with the fluorescentsubstance with respect to the direction of transport, the velocity v oftransport of the fluorescent mark carrier, and the length of time tdfrom the timing at which irradiation of the exciting light isinterrupted to the timing at which the fluorescent afterglow attenuatesby a quantity corresponding to 80% of the maximum possible intensitythereof have a relationship of (L/v≧td), and in that informationrepresented by a fluorescent ink deposit provided on the fluorescentmark carrier being transported is optically read and the fluorescentmark carrier is sorted according to such information.

In order to accomplish the foregoing objects, the twenty-ninth inventionprovides a merchandise sorting apparatus characterized by the provisionof an visible image optical reading means for optically readingdestination information described on a surface of a merchandise to besorted, a fluorescent substance printing means for printing thedestination information on the merchandise with the use of a fluorescentsubstance according to the destination information read by the visibleimage optical reading means, a fluorescent mark optical reading meansfor optically reading information represented by a fluorescent inkdeposit formed by the fluorescent substance printing means, and asorting means for sorting the merchandise according to the destinationinformation read by the fluorescent mark optical reading means.

In order to accomplish the foregoing objects, the thirtieth inventionprovides a merchandise sorting method characterized by the steps ofoptically reading destination information described on a surface of amerchandise with the use of a visible image optical reading means,printing destination information on the merchandise with the use of afluorescent substance according to the destination information read bythe visible image optical reading means, optically reading informationrepresented by a fluorescent ink deposit with the use of a fluorescentmark optical reading means, and sorting the merchandise according to thedestination information read by the fluorescent mark optical readingmeans.

In order to accomplish the foregoing objects, the thirty-first inventionprovides a mark to be detected containing a fluorescent substancecapable of emitting light of a wavelength different from that of anexciting light, which mark is characterized by the provision of a dataarea formed with a pattern corresponding to data to be recorded, and alead-in area formed at a site that is scanned prior to irradiation withthe exciting light upon the data area, said lead-in area continuing asufficient length greater than the longest continuous portion of thepattern formed at the data area.

In order to accomplish the foregoing objects, the thirty-secondinvention provides a method for detecting the mark of the thirty-firstinvention, characterized in that the method comprises a lightirradiating step of projecting light of a substantially constantintensity, an photoelectrically converting step of receiving the lightemitted from a light emitting position and converting it into anelectric signal, a comparison value setting step of automaticallysetting a comparison value from an electric signal corresponding to thelead-in area of the mark, and a mark determining step of comparing adetected value corresponding to the data area in the mark with thecomparison value and determining, in the event that the detected valueexceeds the comparison value, the position at which the mark is formed.

In order to accomplish the foregoing objects, the thirty-third inventionprovides a method of detecting a mark by irradiating the mark,containing the fluorescent substance, with an exciting light andreceiving a fluorescent light emitted from the mark, characterized inthat the method comprises a step of intermittently projecting theexciting light of a substantially constant intensity, a step ofreceiving light, emitted from an irradiating position of the excitinglight, and converting it into an electric signal, an incident lightintensity detecting step of outputting as a comparison value an electricsignal corresponding to the intensity of incident light during anirradiating period, a fluorescent intensity detecting step ofoutputting, as a detected value, an electric signal indicative of themagnitude of a fluorescent component of the incident light, and adetermining step of comparing the detected value with the comparisonvalue and determining, in the event that the detected value exceeds thecomparison value, the position at which the mark is formed.

In order to accomplish the foregoing objects, the thirty-fourthinvention provides an optical reading apparatus for detecting a mark byirradiating the mark to be detected, containing the fluorescentsubstance capable of emitting light of a wavelength different from thatof an exciting light, with the exciting light and receiving afluorescent light emitted from the mark, characterized in that itcomprises a light irradiating means for projecting the exciting light ofa substantially constant intensity intermittently at a predeterminedcycle, a photoelectric converting means for receiving the light emittedfrom a light emitting position and converting it into an electricsignal, a waveform detecting means synchronized with an irradiatingtiming of the light irradiating means for making it possible toindividually detect a minimum value shortly before start of theirradiation, a maximum value shortly before interruption of theirradiation and a detected value immediately after interruption of theirradiation, and a mark determining means for comparing the detectedvalue with a comparison value obtained by dividing the differencebetween the maximum value and the minimum value and for determining, inthe event that the detected value exceeds the comparison value, theposition at which the mark is formed.

In order to accomplish the foregoing objects, the thirty-fifth inventionprovides an optical reading apparatus for detecting a mark byirradiating the mark to be detected, containing the fluorescentsubstance capable of emitting light of a wavelength different from thatof an exciting light, with the exciting light and receiving afluorescent light emitted from the mark, characterized in that itcomprises a light irradiating means for projecting the exciting light ofa substantially constant intensity intermittently at a predeterminedcycle, a photoelectric converting means for receiving the light emittedfrom a light emitting position and converting it into an electricsignal, a waveform shaping means for inverting and amplifying half of anoutput signal from the photoelectric converting means in synchronismwith a timing displaced 90° relative to a period of irradiation by thelight irradiating means, and a low-pass filtering means for selectivelyoutputting a direct current component from the output signal of thewaveform shaping means.

In order to accomplish the foregoing objects, the thirty-sixth inventionprovides an optical reading apparatus for detecting a mark byirradiating the mark to be detected, containing the fluorescentsubstance capable of emitting light of a wavelength different from thatof an exciting light, with the exciting light and receiving afluorescent light emitted from the mark, characterized in that itcomprises a light irradiating means for projecting the exciting light ofa substantially constant intensity intermittently at a predeterminedcycle, a filtering means for selectively receiving a component of lightemitted from a light emitting position, which component has a wavelengthcorresponding to a fluorescent light, a photoelectric converting meansfor converting the light, received through the filtering means, into anelectric signal, a waveform shaping means for inverting and amplifyinghalf of an output signal from the photoelectric converting means insynchronism with a timing displaced 90° from an irradiating period ofthe light irradiating means, a low-pass filtering means for selectivelyextracting a direct current component from an output from the waveformshaping means, and a comparing means for comparing a detected voltageoutputted from the low-pass filtering means with a predetermined voltageand for outputting a detection signal in the event that the detectedvoltage exceeds the predetermined voltage.

In order to accomplish the foregoing objects, the thirty-seventhinvention provides an optical reading apparatus which comprises aprojecting unit for projecting an exciting light necessary to excite afluorescent substance onto a carrier formed with a fluorescent markcontaining the fluorescent substance, a light receiving unit forreceiving a fluorescent light emitted from the fluorescent substance andlight reflected from the carrier and converting them into an electricsignal, an amplifying unit for amplifying the electric signal outputtedfrom the light receiving unit, and a signal detecting unit for detectinginformation recorded by the fluorescent mark from an output signal fromthe amplifying unit, which apparatus is characterized in that theamplifying unit has an amplification factor which is variable accordingto the intensity of the reflected light incident on the light receivingunit and in that the output signal from the amplifying unit which has apeak value lower than a predetermined value is supplied to the signaldetecting unit for analog-to-digital conversion thereof to provide adigital signal corresponding to a pattern in which the fluorescent markis formed.

In order to accomplish the foregoing objects, the thirty-eighthinvention provides an optical reading apparatus which comprises aprojecting unit for projecting an exciting light necessary to excite afluorescent substance onto a carrier formed with a fluorescent markcontaining the fluorescent substance, a light receiving unit forreceiving a fluorescent light emitted from the fluorescent substance andlight reflected from the carrier and converting them into an electricsignal, an amplifying unit for amplifying the electric signal outputtedfrom the light receiving unit, and a signal detecting unit for detectinginformation recorded by the fluorescent mark from an output signal fromthe amplifying unit, which apparatus is characterized in that theamplifying unit has an amplification factor which is variable accordingto the intensity of the reflected light incident on the light receivingunit and the intensity of the fluorescent light and in that the outputsignal from the amplifying unit which has a peak value lower than apredetermined value is supplied to the signal detecting unit foranalog-to-digital conversion thereof to provide a digital signalcorresponding to a pattern in which the fluorescent mark is formed.

In order to accomplish the foregoing objects, the thirty-ninth inventionprovides an optical reading apparatus which comprises a projecting unitfor projecting an exciting light necessary to excite a fluorescentsubstance onto a carrier formed with a fluorescent mark containing thefluorescent substance, a light receiving unit for receiving afluorescent light emitted from the fluorescent substance and lightreflected from the carrier and converting them into an electric signal,an amplifying unit for amplifying the electric signal outputted from thelight receiving unit, and a signal detecting unit for detectinginformation recorded by the fluorescent mark from an output signal fromthe amplifying unit, which apparatus is characterized in that the outputsignal from the amplifying unit is supplied to the signal detecting unitso that the output signal from the amplifying means can be sliced in thesignal detecting unit by two or more slice signals having two or moreslice levels to provide two or more digital signals whereby a digitalsignal corresponding to the fluorescent mark can be obtained bylogically summing the two or more digital signals together.

In order to accomplish the foregoing objects, the fortieth inventionprovides an optical reading apparatus which comprises a projecting unitfor projecting an exciting light necessary to excite a fluorescentsubstance onto a carrier formed with a fluorescent mark containing thefluorescent substance, a light receiving unit for receiving afluorescent light emitted from the fluorescent substance and lightreflected from the carrier and converting them into an electric signal,an amplifying unit for amplifying the electric signal outputted from thelight receiving unit, and a signal detecting unit for detectinginformation recorded by the fluorescent mark from an output signal fromthe amplifying unit, which apparatus is characterized in that an outputsignal outputted from the amplifying unit when an amplification factorthereof is set to a low value and an output signal outputted from theamplifying unit when the amplification factor thereof is set to a highvalue are supplied to the signal detecting unit so that the outputsignals from the amplifying means can be sliced in the signal detectingunit by a slice signal having a particular slice level to provide two ormore digital signals whereby a digital signal corresponding to thefluorescent mark can be obtained by logically summing the two or moredigital signals together.

According to the first, ninth and fourteenth inventions described above,since the fluorescent substance is in the form of ultra-microparticleshaving an average particle size smaller than the wavelength of thefluorescent light of a maximum intensity emitted from the fluorescentsubstance and, in other words, since the wavelength of the fluorescentlight is greater than the particle size of the fluorescent particles,the fluorescent light emitted from the fluorescent particles arrives ata surface of the fluorescent ink deposit having passed through thefluorescent particles positioned thereabove. Accordingly, thefluorescent light can be effectively radiated, detection of thefluorescent light is ensured, and the reliability can be increased.

According to the second, tenth and fifteenth inventions described above,since the fluorescent substance is in the form of ultra-microparticleshaving an average particle size smaller than the wavelength of theexciting light of a maximum intensity emitted from the florescentsubstance and, in other words, since the wavelength of the excitinglight is greater than the particle size of the fluorescent particles,the exciting light can effectively irradiate the fluorescent particlesin a lower region even though the fluorescent particles in an upperregion exist above the lower region. Therefore, the efficiency ofactivation (excitation efficiency) of the fluorescent substance is highand, consequently, detection of the fluorescent light is ensuredaccompanied by an increase in reliability.

According to the third invention, the fluorescent substance comprises,as shown by the general formula (1) or (2), a salt of oxyacidcontaining, as an optical active element, one or more elements selectedfrom the group consisting of Nd, Yb and Er. Even this fluorescentsubstance is in the form of microparticles and, therefore, detection ofthe fluorescent light is ensured accompanied by an increase inreliability.

According to the fourth invention, the fluorescent substance comprises,as shown by the general formula (3), (4) or (5), Fe and Er as an opticalactive element and at least one element selected from the groupconsisting of Sc, Ga, Al, In, Y, Bi, Ce, Gd, Lu and La.

Even this fluorescent substance is a novel fluorescent substance havinga light emission spectrum different from that of the prior artfluorescent substance and is particularly suited for use in a field inwhich security is required.

According to the fifth invention, the fluorescent substance comprises,as shown by the general formula (6), (7) or (8), Yb as an optical activeelement and at least one element selected from the group consisting ofSc, Ga, Al, In, Y, Bi, Ce, Gd, Lu and La.

Even this fluorescent substance is a novel fluorescent substance havinga light emission spectrum different from that of the prior artfluorescent substance and is particularly suited for use in a field inwhich security is required. Also, this fluorescent substance is in theform of generally spheroidal fluorescent particles of substantiallyuniform size with no acicular particles and can therefore be uniformlydispersed in a composition.

According to the sixth and eleventh inventions, the fluorescentsubstance comprises at least one organic substance containing rare earthelement, said organic substance being selected from the group consistingof Nb, Yb and Er and carried with an organic substance such as, forexample, polymethine, anthraquinone, dithiol metal, phthalocyanine,indophenol or azo dyestuff of a kind having an absorption band withinthe infrared region of rays of light. Therefore, the rare earth elementhas a fluorescent output sufficient for a high speed reading and canemit light in response to a variety of wavelength of the exciting light.In other words, in view of the fact that the wavelength of the excitinglight varies depending on the organic substance to be carried, theexciting wavelength (the wavelength of the exciting light required toexcite the fluorescent substance) to be applied to the fluorescentsubstance can ba varied advantageously.

In other words, although the fluorescent substance containing one ormore elements selected from the group consisting of Nb, Yb and Erabsorbs and emits light peculiar to the selected element or elements,the rare earth metal generally has a relatively low light absorptionefficiency as compared with an organic compound and, therefore, additionof an organic compound having an absorption band within the infraredregion of light is effective to increase the light absorption efficiencyto thereby enhance the intensity of light emitted by the rare earthmetal.

Also, in view of the fact that the wavelength of the exciting lightvaries depending on the organic substance to be carried, the excitingwavelength to be applied to the fluorescent substance can baadvantageously varied.

According to the seventh, twelfth and thirteenth inventions, thefluorescent substance contains, as shown by the general formula (9) or(10), at least one of Nb and Yb as an optical active element and, otherthan this optical active element, at least one oxide of Mo or W and analkaline earth metal.

The reason that this fluorescent substance has an excellent waterresistance appears as follows. Namely, while the water solubilitydepends on the magnitude of energies necessary to break the bond betweenanions and cations contained in the material to form a hydrate, that is,the magnitude of a bonding force between the anions and the cations, thebonding force is related to the valence and the coordination number ofthe ions. Accordingly, as compared with a salt having the same anions,the divalent alkaline earth metal exhibits a higher bonding force thanthe monovalent alkaline metal so far as the cations are concerned. Also,if, for example, MoO₄ ²⁻ is chosen for the anion, respectivecoordination numbers of Na and Ca are six and eight, and therefore,CaMoO₄ exhibits a higher bonding force than Na₂MoO₄.

Accordingly, for the same anions, the use of the alkaline earth metalfor the cations is advantageous in respect of the water resistance andthis tendency appears to be maintained even where the rare earth elementis added.

The eighth invention is characterized in that the flux materialcontaining the salt expressed by T₂RO₄.nH₂O is added with at least oneoptical active element selected from the group consisting of Nd and Yb,at least one oxide of one of Mo and W and an alkaline earth metal and isthen calcinated, followed by dissolution of the flux material with asolvent to remove it.

With respect to the particle size of the fluorescent substance soprepared by the calcination referred to above, comparison of the priorart powdery fluorescent substance having a matrix comprised of Na₂MoO₄and mechanically pulverized after the calcination, the powderyfluorescent substance of the present invention having a matrix of CaMoO₄and mechanically pulverized after the calcination and the fluorescentsubstance added with a water-soluble flux material during thecalcination, but with the flux material having been removed by flushingsubsequent to the calcination, have shown that, while the prior artsubstance was of a particle size of about 5 μm at minimum, the substanceof the present invention was found to be microparticles in which primaryparticles of a particle size within the range of about 2 to 5 μm weresecondarily aggregated, and the substance introduced with the fluxmaterial was found to be microparticles of a particle size not greaterthan 1 μm.

In the solid phase reaction induced by the calcination the particle sizeof the starting material is one of factors that determine the particlesize of a reaction product (in this case, the fluorescent substance).The smaller the particle size of the raw material, the smaller theparticle size of the reaction product. Accordingly, the material of aparticle size as small as possible should be chosen for the rawmaterial.

Another one of the factors that determine the particle size of thefluorescent substance is the surface area of contact among the rawmaterials that induce the solid phase reaction. The larger the contactsurface area, the more often the solid phase reaction occurs, resultingin acceleration of the particle growth. By way of example, consideringthe reaction of only the matrix comprised of CaMoO₄ employed in thepresent invention, the solid phase reaction may be expressed by[CaCO₃(s)+MoO₃(s)→CaMoO₄(s)+CO₂(g)]. (In this case, the calcinatingtemperature is 750° C. which is lower than the decompositiontemperature, 900° C., of CaCO₃, but it is suspected that such areaction, [CaCO₃(s)→CaO(s)+CO₃(g)], may occur as a result of somewhatdecomposition.)

If for the flux material Na₂MoO₄ is employed which has a melting pointat 687° C. which is lower than the calcination temperature of 750° C.,the solid phase reaction takes place. CaCO₃ and MoO₃ are dispersed inthe flux melt, accompanied by reduction in surface contact area amongthe raw materials. In view of this, the particle growth appears to bedisturbed, resulting in reduction in particle size of the reactionproduct.

With respect to the light emission intensity, so long as the fluorescentsubstance added with and activated by, for example Nd and Yb isconcerned, when emission outputs exhibited respectively by theconventional fluorescent substance containing Na₂MoO₄ as a matrix, thefluorescent substance of the present invention containing CaMoO₄ as amatrix and the fluorescent substance having a particle size not greaterthan 1 μm, as a result of excitation by the pulsating exciting light arecompared, the fluorescent substance of the present invention hasresulted in reduction of the light emission intensity down to about 80%of that exhibited by the conventional fluorescent substance and thefluorescent substance of the particle size not greater than 1 μm hasresulted in reduction of the light emission intensity down to about 40%of that exhibited by the conventional fluorescent substance.

However, when the sensitivity of an Si photodetector is taken intoconsideration, these emission intensities would bring about no problemin practice. This is because this reduction in emission intensitydiscussed above is attributable to the particle size of the fluorescentsubstance being smaller than that of the conventional fluorescentsubstance and not attributable to the type of matrix material.

The emission intensity and the response are associated with thetransition probability of the rare earth element. Specifically, thehigher the transition probability, the higher emission intensity and thehigher the response. The optical transition of Nd and Yd which are usedin the practice of the present invention as an optical active element isa transition of f-electrons between energy levels and is known as aforbidden transition in terms of the parity of the wave function.

However, in crystals, levels having a parity reverse to the f-trajectorydue to the crystal field are mixed up and the f—f transition ispermitted to a certain extent. This tolerance is large if the symmetricproperty of the crystal field is low and, hence, the transitionprobability is high. By way of example, while Na₂MO₄ employed in theconventional fluorescent substance is of a cubic system, CaMO₄ employedin the practice of the present invention is of a pyramidal quadraticsystem and, therefore, the symmetric property of the crystal is low.Accordingly, in terms of material, the fluorescent substance of thepresent invention cannot be considered inferior to the conventionalfluorescent substance in respect of the emission intensity and theresponse.

Also, the response does not depend on the particle size, and thefluorescent substance of the present invention which is consideredhaving a high transition probability exhibits a somewhat higherresponse.

According to the sixteenth invention, since the content of thefluorescent particles in the fluorescent ink deposit formed by printingis greater than 1 wt %, but smaller than 30 wt %, the presence of theink deposit is not noticeable in sight and, therefore, the ink depositwill not adversely affect the appearance of the fluorescent markcarrier. Accordingly, it is suited for the fluorescent mark carrier tohave a security.

According to the seventeenth invention, since the fluorescent inkdeposit formed by printing has a thickness not greater than 35 times theparticle size of the fluorescent particles, the presence of the inkdeposit is not noticeable in sight and, therefore, the ink deposit willnot adversely affect the appearance of the fluorescent mark carrier.Accordingly, it is suited for the fluorescent mark carrier to have asecurity.

According to the fluorescent composition of the eighteenth invention,since the binder for dispersing and retaining the fluorescentmicroparticles has a light transmissivity with respect to each of theexciting and fluorescent light being not lower than 80%, entry of theexciting light into the fluorescent ink deposit and exit of thefluorescent light generated internally of the fluorescent ink deposit tothe outside take place efficiently. Because of this, assured detectionof the fluorescent light is possible, accompanied by increase inreliability.

According to the fluorescent mark carrier of the nineteenth invention,the fluorescent particles in the fluorescent mark carrier are depositedon a fiber aggregation having minute surface irregularities such as, forexample, paper, and therefore the fluorescent ink deposit has a surfaceformed with corresponding minute surface irregularities. If thefluorescent ink deposit containing the fluorescent particles are formedon a smooth surface such as, for example, a synthetic film, the surfaceof the ink deposit will become smooth. If this smooth surface of thefluorescent ink deposit is irradiated with the exciting light, portionof the exciting light will undergo a regular reflection and will nolonger activate the fluorescent substance. However, deposition of thefluorescent particles on the fiber aggregation such as accomplished inthe present invention is effective to substantially eliminate such aregular reflection of the exciting light and, therefore, the efficiencyof excitation of the fluorescent substance is high.

According to the fluorescent mark carrier of the twentieth invention,since the fluorescent ink deposit in the fluorescent mark carrier has a20% or lower visible ray absorption characteristic, the fluorescent inkdeposit is substantially colorless and transparent and, for this reason,it will not adversely affect the appearance of the fluorescent markcarrier and is suited for use where security is of great importance.

According to the optical reading apparatus of the twenty-firstinvention, the mirror has a portion thereof provided with a lighttransmitting region for allowing a substantially entire quantity of theexciting light from the light emitting element to pass therethrough.Therefore, as compared with the semitransparent mirror employed in theconventional optical reading apparatus, the quantity of the excitinglight used to irradiate the fluorescent substance can be increased, withactivation of the fluorescent substance enhanced effectively.

Moreover, the quantity of the fluorescent light reflected by the mirroris relatively large as compared with that reflected by thesemitransparent mirror. For this reason, detection of the fluorescentlight is ensured and the reliability can be increased.

According to the optical reading apparatus of the twenty-secondinvention, since the pattern of the exciting light emitted from thelight emitting element is elliptical with its major axis extending in adirection lengthwise of the bar code, the area of the illuminatedsurface increased as compared with the conventional round pattern of theexciting light (that is, assuming that the diameter of the round patternis equal to the length of the minor axis of the elliptical pattern). Forthis reason, the intensity of the light emitted is high, making itpossible to accomplish an assured detection of the fluorescent lightaccompanied by increase in reliability.

With the optical reading apparatus of the twenty-third invention, sincethe velocity v of transport of the fluorescent mark carrier is regulatedby the relationship between the length d of the opening in the slitmember and the rise time tu, only the information desired to be read(for example, a single bar code) can be assuredly read out with no timewasted. For this reason, the reliability in reading can be increased,making it possible to accomplish a high speed reading.

With the optical reading apparatus of the twenty-fourth invention, sincethe velocity v of transport of the fluorescent mark carrier is regulatedby the relationship the interval between neighboring portions printedwith the fluorescent substance and the fall time td, only theinformation desired to be read can be assuredly read out with nopossibility of being adversely affected by the fluorescent afterglowfrom the neighboring bar and, therefore, the reliability can beincreased.

In the optical reading apparatus according to the twenty-fifthinvention, the provision is made of the slit member between the secondconvex lens and the light receiving element wherefore, even though thethickness of the fluorescent mark carrier caries to a certain extent,the fluorescent mark carrier can be satisfactorily transported withoutdamaging the slit member.

According to the twenty-sixth invention, the semiconductor laser diodehaving an excellent light collecting ability and also an excellent lightdirectivity is employed for the light emitting element and, for thedrive circuit for driving the semiconductor laser diode, the circuithaving an automatic power control function so that the exciting light ismonitored to control output conditions of the exciting light beingemitted from the laser diode. Therefore, both of the pulse interval andthe pulse intensity of the exciting light are fixed to make it possibleto provide the optical reading apparatus stabilized in operation.

According to the twenty-seventh invention, since the relationship amongthe velocity v of transport of the fluorescent mark carrier, the lengthd of the opening in the slit member and the rise time tu are uniquelydefined, it is possible to provide a high speed reading system capableof reading out only the information desired to be read with no timewasted.

According to the twenty-ninth invention, since the relationship amongthe velocity v of transport of the fluorescent mark carrier, theinterval L between neighboring portions printed with the fluorescentsubstance and the fall time td is uniquely defined, it is possible toprovide a highly reliable reading system capable of reading only theinformation desired to be read with no possibility of being adverselyaffected by the fluorescent afterglow from the neighboring bar.

Since each of the twenty-ninth and thirty inventions is so constructedas hereinbefore described, a merchandise sorting can be automatically,efficiently and assuredly accomplished.

According to each of the thirty-first and thirty-second inventions,since the lead-in area of the fluorescent mark has a length sufficientlygreater than the longest continuous portion of the pattern formed at thedata area, the intensity of the fluorescent light emitted from thatlead-in area is higher and more stabilized than the data area and iscomparable to the intensity proper to particular detecting condition orenvironments.

Moreover, since that lead-in area is defined at a location adjacent aportion of the data area which is first scanned and is continued to thedata area, that lead-in area works together with the data area so as toprovide a substantially constant contrast over the entire region of thedata area and the intensity of the fluorescent light emitted from thedata area can vary uniformly over the entire region of the data area.

Therefore, by initially detecting the intensity of the fluorescent lightat the lead-in area and then comparing the intensity of the fluorescentlight emitted from the data area with a reference value represented bythe intensity of the fluorescent light from the lead-in area, thecontents of the mark formed at the data area can advantageously bedetermined accurately.

In the optical reading apparatus according to each of the thirty-thirdand thirty-fourth inventions, when the mark is irradiated by the lightfrom the light irradiating means, not only does the mark reflect theincoming light, but also an irradiated portion of the mark emits thefluorescent light of a particular wavelength. The incident lightcontaining the reflected component and the fluorescent component ispassed through the optical filtering means to selectively extract thelight of a wavelength equal to that of the fluorescent length and issubsequently converted into an electric signal by the photoelectricconverting means so that the electric signal can be processed by thewaveform detecting means.

In the waveform detecting means, the magnitude of the amplitude of theincident and the intensity of the fluorescent light are detectedindividually. Therefore, by preparing a comparison value which varieswith change in intensity of the incident light and allowing the markdetermining means in the subsequent stage to compare the detected valuewith the comparison value, the comparison value can be automatically setto an optimum value according to change in intensity of the incidentlight itself.

Moreover, by allowing a signal input determining means to determine atall times the intensity of the incident light and to initiate adetermining operation only when the significant incident light isdetected, only genuine data are used as a detected value and acomparison value and, therefore, the reliability can be increasedadvantageously.

In the optical reading apparatus according to each of the thirty-fifthand thirty-sixth invention, when the pulsating light from the lightirradiating means is projected onto the mark at a predetermined timing,light from that portion of the mark on which the light impinges entersthe optical filtering means. The light incident on the optical filteringmeans contains external light having a random distribution ofwavelength, but having an intensity of a substantially constant level,reflected light having a distribution of wavelength that can bespecified, but having an intensity that varies in a fashion representedby a rectangular wavelength, and fluorescent light having a particularwavelength different from that of the reflected light, but having aintensity that varies with irradiation of the light.

Therefore, the use of the optical filtering means is effective toselectively pass the light of a wavelength equal to that of thefluorescent light therethrough so that the other light components thanthe fluorescent light can be attenuated down to a value as small aspossible, thereby making it possible for the photoelectric convertingmeans to convert the intensity of the light into an electric signal of amagnitude proportional to such intensity of the light.

While the external light has a substantially constant intensity, thereflected light has a cyclically varying intensity of a substantiallyconstant level. On the other hand, the fluorescent light has anintensity that varies according to the irradiating light at the sametiming as the reflected light. In other words, the fluorescent lightjust emitted and the fluorescent afterglow attain a maximum intensitywhen the irradiating light is switched off, and a minimum intensity whenthe irradiating light is switched on.

Accordingly, if the waveform shaping means is so designed so as toinvert and amplify the input signal, inputted during a period ofirradiation, at a timing shifted 90° relative to the period ofirradiation, the half period during which both of the emitted light andthe fluorescent afterglow are relatively high can be obtained in theform of a change in positive voltage whereas the half period duringwhich they are relatively low can be obtained in the form of a change innegative voltage.

In the meantime, while each of the external light and the reflectedlight gives rise to positive and negative voltages that are equal toeach other, the electric signal indicative of the fluorescent light isso inverted that the difference between the both can be maximized.Accordingly, when the electric signal is passed through the low-passfiltering means in the subsequent stage, both of the external light andthe reflected light are cancelled, but the fluorescent light ifcontained gives rise to the difference between the positive and negativesignals which is extracted as a direct current voltage. Therefore, if itis determined that the difference between the direct current voltagewith a preset value set in a comparator is significant, a mark signalindicative of the position of the mark is outputted.

In the optical reading apparatus according to any one of thethirty-seventh to fortieth inventions, the level and amplitude of theanalog reproduction signal vary considerably depending on surfaceproperties of the carrier on which the fluorescent mark is formed. Onthe other hand, the level and amplitude of this analog reproductionsignal can be properly adjusted by varying the amplification factor ofthe amplifying unit. In view of this, if the amplification factor of theamplifying unit can be switched depending on the intensity of thereflected light incident upon a light receiving unit and the level ofthe analog reproduction signal is matched with a predetermined slicesignal level set in the signal detecting unit, a desired binary signalcan be obtained with a slice signal of a predetermined level regardlessof the properties of the carrier and, therefore, information associatedwith the fluorescent marks on the carriers of a varying material can beprecisely read out with the single reading apparatus.

Also, if the amplification factor of the amplifying unit is adjustableto one of different values depending on the intensity of the reflectedlight and that of the fluorescent light both incident upon the lightreceiving unit, it is possible to match the level of the analogreproduction signal with that of the slice signal as accurately aspossible and, therefore, the reading of the fluorescent mark signal canbe accomplished highly precisely.

On the other hand, where the analog reproduction signal detected from aseries of fluorescent marks formed on one and the same carrier varies inlevel, no accurate reading of the fluorescent mark information ispossible with the previously described first and second means.Accordingly, if the analog reproduction signal supplied to the signaldetecting unit is sliced by two or more slide signals having two or moreslice levels appropriate to the level variation, the binary signal ofthe analog reproduction signal for each level can be obtained. If alogical sum of the binary signals for those levels is calculated, thebinary signal corresponding to the entire analog reproduction signal canbe obtained. Thus, even though the analog reproduction signal detectedof the series of the fluorescent marks formed on one and the samecarrier accompanies a partial level variation, the fluorescent markinformation can be read out accurately.

Also, in a similar situation, even if without the analog reproductionsignal being sliced by the two or more slice signals, the amplificationfactor is adjusted according to each of the levels of the analogreproduction signals so that the analog reproduction signal can besliced by a slice signal having a particular slice level, the binarysignals of the analog reproduction signals for those levels can beobtained. Even in this case, if a logical sum of the binary signals forthose levels is calculated, the binary signal corresponding to theentire analog reproduction signal can be obtained.

By way of example, with respect to the analog reproduction signal of ahigh level, this analog reproduction signal is sliced by a particularslice signal with the amplification factor lowered. At this time, nodigitization takes place of the analog reproduction signal of a lowlevel. On the other hand, with respect to the analog reproduction signalof the low level, this analog reproduction signal is sliced by theparticular slice signal with the amplification factor increased. At thistime, no digitization takes place of the analog reproduction signal ofthe high level. Accordingly, by taking the logical sum of these binarysignals, the binary signal corresponding to the entire analogreproduction signal can be obtained.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram showing an emission spectrum exhibited by a complexsalt of cinnamic acid with neodymium and ytterbium (1/1) according to anembodiment of the present invention;

FIG. 2 is a characteristic graph showing the relationship between themolar ratio of Nd/Yb contained in the complex salt of cinnamic acid withneodymium and ytterbium (1/1) and the emission intensity;

FIGS. 3A, 3B and 3C are characteristic graphs showing the irradiationtiming of an exciting light and respective conditions of emission offlorescent light from two types of fluorescent substances;

FIG. 4 is a schematic diagram showing the relationship among the slitlength in a slit member, the velocity of transport of a fluorescent markcarrier and the intervals of fluorescent ink deposits on the carrier;

FIG. 5 is a graph showing the relationship among the viscosity of aninking medium of the present invention for use with an ink jet printeraccording to the present invention, a relative output and the degree ofvariability of the size of a droplet of the inking medium;

FIG. 6 is a graph showing the relationship among the surface tension ofthe inking medium of the present invention for use with the ink jetprinter and the degree of variability of the size of the ink droplet;

FIG. 7 is a graph showing the relationship between the specificresistance of the ink droplet and the degree of variability of the inkdroplet;

FIG. 8 is a graph showing the relationship between the pH value of theinking medium of the present invention for use with the ink jet printerand the dispersion stability;

FIG. 9 is a chart showing charge stocks of various fluorescentsubstances in respective samples 1 to 7 and mixing ratios thereof;

FIG. 10 is a chart showing charge stocks of various fluorescentsubstances in respective samples 8 to 15 and mixing ratios thereof;

FIG. 11 is a chart showing calcination temperature, composition andparticle size of the various fluorescent substances in the respectivesamples 1 to 7;

FIG. 12 is a chart showing calcination temperature, composition andparticle size of the various fluorescent substances in the respectivesamples 8 to 15;

FIG. 13 is a diagram showing an emission spectrum of the fluorescentsubstance in the sample 1 according to an embodiment of the presentinvention;

FIG. 14 is a diagram showing an emission spectrum of the fluorescentsubstance in the sample 7 according to an embodiment of the presentinvention;

FIG. 15 is a diagram showing an emission spectrum of the fluorescentsubstance in the sample 17 which pertains to a comparison;

FIG. 16 is a chart showing charge stocks of various fluorescentsubstances in respective samples 16 to 20, which pertain to respectiveembodiments of the present invention, mixing ratios thereof andcalcination temperatures;

FIG. 17 is a diagram showing an emission spectrum exhibited by thefluorescent substance, (ErY)₃(FeAl)₅O₁₂, in the sample 16 according tothe embodiment of the present invention;

FIG. 18 is a graph showing a pattern of distribution of spectralsensitivity of a Ge photodiode;

FIG. 19 is a graph showing a pattern of distribution of spectralsensitivity of an InGaAs photodiode;

FIG. 20 is a chart showing charge stocks of various fluorescentsubstances in respective samples 21 to 25, which pertain to respectiveembodiments of the present invention, mixing ratios thereof andcalcination temperatures;

FIG. 21 is a diagram showing an emission spectrum exhibited by thefluorescent substance, Yb_(0.3)Y_(2.7)Al₅O₁₂, in the sample 21 accordingto the embodiment of the present invention;

FIG. 22 is a graph showing a change in emission intensity with change inmolar ratio X of Yb in the fluorescent substance, Yb_(X)Y_(1−X)Al₅O₁₂,according to the embodiment of the present invention;

FIG. 23 is a diagram showing an emission spectrum of the fluorescentsubstance according to Example 12;

FIG. 24 is a photographic reproduction of a waveform of a response ofthe fluorescent substance in Example 12 to a pulsating exciting light;

FIG. 25 is a microphotograph showing a particle structure of thefluorescent substance in Example 12;

FIG. 26 is a graph showing a change in recovery with passage of timewhich is exhibited when the fluorescent substances in Examples 12 and 9were immersed in a pure water;

FIG. 27 is a schematic perspective view showing the principle of anelectric field control system used in the practice of an ink jetrecording process;

FIG. 28 is a plan view of a postal envelope formed with a fluorescentmark according to an embodiment of the present invention;

FIG. 29 is a plan view showing another example of the postal envelopeformed with the fluorescent mark according to the embodiment of thepresent invention;

FIG. 30 is a flowchart showing the manner in which a bar codeinformation is applied to postal matter and the bar code so applied isread out;

FIG. 31 is a schematic diagram showing a first embodiment of an opticalreading apparatus of the present invention;

FIG. 32 is a plan view of a mirror used in the optical reading apparatusshown in FIG. 31;

FIG. 33 is a fragmentary side sectional view of a portion of the opticalreading apparatus, showing a function of a slit member;

FIG. 34 is a schematic perspective view showing a pattern of a laserbeam outputted from a semiconductor chip used in this embodiment of thepresent invention;

FIG. 35 is a diagram used to explain the relationship between thepattern of the laser beam and a pattern of bar codes printed;

FIG. 36 is a diagram used to explain the relationship between thepattern of the laser beam and the pattern of inclined bar codes;

FIG. 37 is a plan view of a reflecting mirror used in a secondembodiment of the optical reading apparatus;

FIG. 38 is a fragmentary side sectional view of a portion of the opticalreading apparatus utilizing the reflecting mirror showing FIG. 37;

FIG. 39 is a schematic diagram used to explain how an Example 3 of theoptical reading apparatus is used;

FIGS. 41A, 41B and 41C are schematic diagrams used to explain how theExample 3 of the optical reading apparatus is used;

FIG. 41 is a timing chart showing the relationship between the timing ofemission of a light emitting element and conditions of output from alight receiving element in the practice of a detecting method utilizingfluorescent afterglow;

FIG. 42 is a schematic block diagram showing an Example 4 of the opticalreading apparatus;

FIG. 43 is a diagram showing a structure of a semiconductor laser diodeused in the optical reading apparatus;

FIG. 44 is a schematic diagram showing a basic structure of an Example 5of the optical reading apparatus;

FIGS. 45A, 45B, 45C and 45D are explanatory diagrams showing respectiveconditions in which marks are formed;

FIG. 46 is a block diagram showing an entire structure of the opticalreading apparatus;

FIGS. 47A, 47B and 47C illustrate a diagram showing how the mark isdetected;

FIG. 48 is a flowchart showing the sequence of operation of a markdetecting unit;

FIG. 49 is a schematic block diagram showing a basic structure of anExample 6 of the optical reading apparatus;

FIG. 50 is a block diagram showing an entire structure of the opticalreading apparatus shown in FIG. 49;

FIG. 51 is a block diagram showing the details of the mark detectingunit used in the apparatus shown in FIG. 50;

FIGS. 52A through 52H illustrate a timing chart showing the relationshipamong various signals appearing in the optical reading apparatus of FIG.50;

FIG. 53 is a schematic diagram showing a basic structure of an Example 7of the optical reading apparatus;

FIG. 54 is a block diagram showing an entire structure of the opticalreading apparatus shown in FIG. 53;

FIG. 55 is a block diagram showing the details of the mark detectingunit used in the apparatus shown in FIG. 54;

FIGS. 56A through 56F illustrate a timing chart showing the relationshipamong various signals appearing in the optical reading apparatus of FIG.54;

FIG. 57 is a side sectional view, on an enlarged scale, of a markcarrier showing the mark, an adhesive layer and a protective sheet;

FIG. 58 is a block diagram showing an Example 8 of the optical readingapparatus;

FIG. 59 is a schematic diagram showing the manner in which the opticalreading apparatus of FIG. 58 is arranged;

FIG. 60 is a flowchart showing the sequence of reading of the markexecuted by the optical reading apparatus of FIG. 58;

FIGS. 61A and 61B are diagrams showing waveforms of analog reproductionsignals given by the optical reading apparatus of FIG. 58;

FIG. 62 is a flowchart showing the sequence of reading of the markexecuted by the optical reading apparatus;

FIG. 63 is a schematic diagram showing the manner in which an Example 9of the optical reading apparatus is arranged;

FIGS. 64A and 64B are diagrams showing waveforms of analog reproductionsignals given by the optical reading apparatus of FIG. 63;

FIG. 65 is a circuit diagram showing amplifying and signal detectingunits used in an Example 10 of the optical reading apparatus;

FIG. 66 is a diagram showing waveforms of an analog reproduction signaloutputted from a first differential amplifier used in the opticalreading apparatus of FIG. 63;

FIG. 67 is a diagram showing waveforms of an analog reproduction signaloutputted from a second differential amplifier used in the opticalreading apparatus of FIG. 63;

FIGS. 68A through 68E are diagrams showing waveforms of binary signalsoutputted from various units of the optical reading apparatus of FIG.63;

FIG. 69 is an explanatory diagram showing how the signal is digitized toprovide the binary signal in an Example 11 of the optical readingapparatus;

FIG. 70 is an explanatory diagram showing the structure of the prior artoptical reading apparatus; and

FIG. 71 is a diagram showing analog reproduction signals appearing inthe prior art optical reading apparatus.

BEST MODES FOR CARRYING OUT THE INVENTION

For the purpose of easy understanding of the present invention, thepresent invention will be described under the following headings:

1. Fluorescent Substance and Fluorescent Composition

2. Method of Printing Fluorescent Composition and Fluorescent MarkCarrier

3. Optical Reading Apparatus and Optical Reading System

1. [Fluorescent Substance and Fluorescent Composition]

Fluorescent Composition 1

The fluorescent substance of the present invention is an organicmetallic compound containing, as an optical active element, at leastneodymium (Nd), or preferably an organic metallic compound containing,as an optical active element, a mixture of Nd and ytterbium (Yb). Anorganic material of this organic metallic compound is at least oneorganic material selected from the group consisting of carboxylic acid,ketone, ether and amine.

More specifically, the organic metallic compound referred to above maybe at least one organic metallic compound selected from the groupconsisting of neodymium cinnamate, a complex salt of cinnamic acid withneodymium and ytterbium, a complex salt of benzoic acid with neodymiumand ytterbium, neodymium naphthoate and a complex salt of naphthoaicacid with neodymium and ytterbium. Of them, a complex salt of carboxylicacid comprising a cinnamic acid and Nd and Yb is preferred.

The molar ratio of Nd relative to Yb (Nd:Yb) is preferably selectedwithin the range of 9.5:5 to 3:7 and more preferably within the range of9:1 to 5:5, by the reason which will become clear from the subsequentdescription made with reference to FIG. 2.

This fluorescent substance may be synthesized in any suitable manner,but the use of an ion-exchange reaction in an aqueous solution, such aspublished by M. D. Taylor, et al., in J. Inorg. Nucl. Chem., 30,1530-1511 (1968), or an elimination reaction of isopropoxide in anon-polarity solvent such as published by P. N. Kapoor, et al., inSynth. React. Inorg. Met. -Org. Chem., Vol. 17, 507-523 (1987), ispreferred for synthesization of the fluorescent substance.

Unlike an inorganic fluorescent substance, this organic fluorescentsubstance contains in its molecules an organic material such ascarboxylic acid, β-diketone, cyclic ether or cyclic amine, and inparticular, cinnamic acid which is one kind of the carboxylic acids ispreferred because it has an excellent chemical stability and gives riseto a relatively high emission output.

This fluorescent substance has an average primary particle size notgreater than about 80% of the wavelength (810 nm) of the infrared rays,that are used as exciting light, at the maximum intensity thereof andnot greater than about 70% of the wavelength (980 nm) of the fluorescentlight, emitted from such fluorescent light, at the maximum intensitythereof. Since this fluorescent substance does not form a block ofprimary particles such as observed in the inorganic fluorescentsubstance and will not damage crystals thereof, it can easily bepulverized and will become finer when dispersed in a binder. Therefore,when an inking medium for use with the ink jet printer is to be preparedusing this organic fluorescent substance, the latter is satisfactorilystabilized having been dispersed in the binder with no substantialpossibility of being precipitated and, therefore, the use of such inkingmedium will not result in a nozzle clogging or an insufficient jettingof droplets of the inking medium.

A specific methods of making the fluorescent substance will now bedescribed.

1.24 g (8.37 mol) of cinnamic acid and 0.37 g (8.37 mol) of sodiumhydroxide are added to 120 ml of ion-exchange water while being stirred,to provide an aqueous solution of sodium cinnamate. The pH value of thisaqueous solution is adjusted to 10 by the use of an aqueous solution of0.1N sodium hydroxide.

Separately therefrom, 0.54 g (1.39 mol) of neodymium chloridehexahydrate and 0.54 g (1.39 mol) of ytterbium chloride hexahydrate aredissolved completely in 50 ml of ion-exchange water to provide anaqueous solution which is subsequently added, while being stirred, tothe aqueous solution of sodium hydroxide. This addition results information of sediment.

Thereafter, the Ph value of the reaction liquid is adjusted to 5 by theaddition of 0.1N hydrochloric acid and is stirred for two hours,followed by filtration of the sediment to obtain a filtrate. Thefiltrate is, after having been washed, dried at 120° C. for 5 hours toprovide 1.62 g of a complex salt of cinnamic acid with neodymium andytterbium (1/1). This quantity of the resultant fluorescent substancecorresponds to the yield of 93.1%.

FIG. 1 illustrates an emission spectrum exhibited by the complex salt ofcinnamic acid with neodymium and ytterbium (1/1) when the latter isexcited by exciting light emitted from a GaAlAs light emitting diodeused as a source of excitation, showing the maximum peak wavelengthappearing at about 980 nm.

FIG. 2 illustrates a characteristic graph showing the relationshipbetween the molar ratio of Nd relative to Yb (Nd/Yb) and the emissionintensity. As shown therein, a high emission output is exhibited whenthe Nd/Yb molar ratio is within the range of 9.5/5 to 3/7 and preferablywithin the range of 9/1 to 5/5.

The complex salt of cinnamic acid with neodymium and ytterbium (1/1) hasan average particle size of 0.2 μm which corresponds to about 25% of thewavelength (0.81 μm) of the maximum intensity of the exciting light andabout 20% of the wavelength (0.98 μm) of the maximum intensity of thefluorescent light emitted by the complex salt of cinnamic acid withneodymium and ytterbium (1/1) and which is thus extremely smaller thanthe wavelength of the maximum intensity of any one of the exciting lightand the fluorescent light.

The above discussed method may be equally employed to prepare a complexsalt of benzoic acid with neodymium and ytterbium and this can beaccomplished if cinnamic acid used in the practice of the abovediscussed method is replaced with benzoic acid. Even the resultantfluorescent substance, that is, complex salt of benzoic acid withneodymium and ytterbium, has an average particle size which is extremelysmaller than the wavelength of the maximum intensity of any one of theexciting light and the fluorescent light.

The fluorescent substance in the form of super microparticles of anorganic metallic compound such as, for example, neodymium cinnamate,neodymium naphthoate, complex salt of naphthoeic acid with neodymium andytterbium or neodymium benzoate may be equally employed.

Since the wavelength of the maximum intensity of the exciting light usedto excite any of those fluorescent substances and the wavelength of themaximum intensity of the fluorescent light emitted therefrom exceedabout 0.8 μm (800 nm), the use of the fluorescent substance having anaverage particle size not greater than 0.8 μm results in an effectiveentry of the exciting light and an effective emission of the fluorescentlight.

FIG. 3 illustrates characteristic graphs showing a condition of theexciting light being irradiated and a condition of the fluorescent lightemitted from the fluorescent substance. FIG. 3(a) illustrates thecondition of irradiation from the GaAlAs light emitting diode and theexciting light emitted therefrom is generally in the form of a train ofpulses having a pulse repetition period of 2,000 μsec.

FIG. 3(b) illustrates the condition of emission of the fluorescent lightfrom the complex salt of cinnamic acid with neodymium and ytterbium(1/1), prepared by the previously discussed method, showing that therise time tu required for the intensity of the fluorescent light emittedthereby subsequent to the start of irradiation of the exciting light toattain 90% of the maximum intensity thereof is about 100 μsec. Also, thefall time td required for the intensity of the fluorescent afterglowsubsequent to the interruption of irradiation of the exciting light toattenuate by a quantity corresponding to 80% of the maximum intensity ofthe fluorescent light is about 50 μsec. Thus, both of the rise time tuand the fall time td are smaller than 200 μsec, showing an extremelyhigh response.

FIG. 3(c) illustrates the condition of emission of the fluorescent lightfrom the fluorescent substance which is LiNd_(0.5)Yb_(0.5)P₄O₁₂, showingthat the rise time td is about 1,300 μsec and the fall time td is about1,000 μsec, both of them being considerably greater than 200 μsec. Ifthe rise time tu of the fluorescent substance is smaller than 200 μsecas discussed above, the length of time required for the light receivingelement to receive light subsequent to the start of irradiation of theexciting light is extremely small and, accordingly, a reading of afluorescent mark formed by the use of the fluorescent substance can beaccomplished at a high speed.

Also, when as shown in FIG. 4 information is to be read out by anoptical reading apparatus 25 from a fluorescent mark in the form of apattern of bar codes defined by fluorescent ink deposits 18 formed byprinting a fluorescent inking medium while a fluorescent mark carrier 10bearing such fluorescent mark is transported in one direction, thefluorescent substance contained in each fluorescent ink deposit 18 isactivated by irradiating the fluorescent mark by the exciting light 60emitted from the light emitting element incorporated in the opticalreading apparatus 25 to cause the fluorescent substance to emit from therespective ink deposit 18 the fluorescent light 61 which is subsequentlyreceived by the light receiving element in the optical reading apparatus25 for reading of the bar code information.

It is to be noted that reference numeral 32 represents a slit memberdisposed on an optical path through which, as will become clear from thesubsequent description, the exciting light 60 is projected onto thefluorescent ink deposits 18 one at a time and the resultant fluorescentlight 61 from the respective fluorescent ink deposit 18 travels towardsthe light receiving element in the optical reading apparatus 25.Assuming that the speed v of transport of the fluorescent mark carrier10 is expressed by v, the length of a slit 32 a defined in the slitmember 32 as measured in a direction conforming to the direction oftransport is expressed by d and the rise time of the fluorescentsubstance is expressed by tu, and if arrangement is made to establishthe relationship of (tu≦d/v), information represented by eachfluorescent ink deposit 18 on the fluorescent mark carrier beingtransported can assuredly be read only when such fluorescent ink deposit18 is brought into alignment with the slit 32 a of the slit member 32.If, however, the rise time tu of the fluorescent substance is greaterthan d/v, the respective ink deposit 18 will pass underneath the slit 32a without giving rise to a sufficient intensity of the fluorescent lightand, accordingly, the light receiving element will provide an output solow as to result in a problem in reliability.

Also, referring still to FIG. 4, if arrangement is made to establish therelationship of (td≦L/v) wherein L represents the interval between theneighboring fluorescent ink deposits (for example, bars) 18 as measuredin a direction conforming to the direction of transport of thefluorescent mark carrier 10 and td represents the fall time of thefluorescent substance, an accurate reading of the bar code informationis possible. If the fluorescent substance having a relatively long falltime td, that is, the fluorescent substance capable of giving afluorescent afterglow for a relatively long time, is employed, thefluorescent afterglow emanating from one of the fluorescent ink deposits18 that precedes the fluorescent ink deposit 18 having moved past aposition aligned with the slit 32 a may also be read and, therefore, anaccurate reading of the code information cannot be accomplished.

In contrast thereto, the use of the fluorescent substance having thefall time td that is extremely small as shown in FIG. 3(b) is employed,the problem such as discussed above can be eliminated, making itpossible to accomplish an accurate reading of the code information andalso to reduce the interval L between the neighboring ink depositsforming the code bars to thereby reduce the area in which thefluorescent mark is formed.

The use of an organic binder having a density ρ2 which satisfies therelationship of (ρ1/ρ2≦1.8) wherein ρ1 represents the density of thefluorescent substance is effective to eliminate such a problem that theamount sediment of the fluorescent microparticles in the inking mediumis so small that, when the fluorescent ink deposit is formed, thefluorescent microparticles may be concealed having been covered by afilm of binder to an extent as to prevent the fluorescent light frombeing quickly surfaced.

The content of the binder in the fluorescent ink deposit must be equalto or greater than 5 wt %. If the content of the binder is smaller than5 wt %, the fluorescent particles may separate and, for this reason,printing of the bar code will become incomplete to such an extent as topose a difficulty in properly retaining the information. In view ofthis, the content of the binder is required to be equal to or greaterthan 5 wt %.

For a water-soluble organic binder, acrylic resin or an acrylic resinhaving, in its side chain, an ester group or polyether may be employed.Other than these examples, polyvinyl alcohol, polyvinyl pyrrolidone,carboxymethylcellulose, starch, a formalin condensate of naphthalenesulfonate or polystyrene sulfonate may also be employed.

For a non-water-soluble organic binder, a phenol resin such as, forexample, novolak-type phenol, resol-type phenol, rosin-modified phenolor alkyl-modified phenol, a water-added rosin or a rosin resin such as,for example, polyethylene glycol ester, polyfunctional alcohol ester orrosin glycerin ester may be employed.

For a solvent, one or a mixture of water, alcohol, ketone, ester, ether,a solvent of aromatic hydrocarbon and a solvent of fatty hydrocarbon maybe employed.

An electrolyte used as a electroconductivity imparting agent may beLiNO₃, LiCl, KCl, NaCl or KNO₃.

For a stabilizer, one or a mixture of alkyl phthalate (for example,dioctyl phthalate or dibutyl phthalate), aryl phthalate, glycol(ethylene glycol, propylene glycol, polyethylene glycol or polypropyleneglycol) and glycol ester may be employed.

A defoaming agent used may be a silicone type, a silica-silicone type, ametallic soap, an amide type, or a polyether type.

One or more dyes may also be employed. Examples of the dyes includeDirect Black GW, Capamine Black ESA, Rodamine B, Rodamine 7G, methyleneblue, Direct Fast Orange, Complantine Green G, Milling Yellow O andKatione Pink FG.

A specific composition of the inking medium for use with an ink jetprinter will now be illustrated.

Complex salt of cinnamic acid with neodymium 80 parts by weight andytterbium (0.2 in average particle size) Phthalocyanine blue 1 part byweight Cation-type acrylic resin 20 parts by weight Polyethylene glycol1 part by weight Dioctyl phthalate 0.5 part by weight KCl 0.5 part byweight Defoaming agent 0.4 part by weight Water 100 parts by weightEthanol 20 parts by weight

The composition was mixed and dispersed in a sand mill for one hour toprovide the fluorescent inking medium for use with the ink jet printerwhich was subsequently used in the ink jet printer to accomplish aprinting of characters on a paper.

Observation on the printed characters has indicated that no ink runoccurred and that the characters were printed precisely in a blue color.

To detect the printed characters optically, 100 identical reading testswere carried out at a reading speed of 4 m/sec by irradiating theprinted characters by the exciting light having a maximum intensity inthe vicinity of a wavelength of 970 nm to emit fluorescent light whichwas then received by a silicon photodiode detector. As a result, theinformation was assuredly read out each time the reading test wasconducted.

It is to be noted that in the above described composition of the inkingmedium, the amount of any one of phthalocyanine blue, polyethyleneglycol, dioctyl phthalate, water and ethanol added may be eitherincreased or decreased if desired and that the use of one or more ofthem may be dispensed with if desired.

As listed in the above table of composition of the inking medium, ifwhere water is employed for the solvent an easily volatilizeable organicliquid such as, for example, alcohol having a compatibility with wateris employed in combination with water, the resultant fluorescentcomposition is quick to dry and is, therefore, effectively utilized whensuch fluorescent composition is to be printed on, for example, papersand, in particular, where a relatively large amount of the solvent isemployed such as that used with the ink jet printer.

In the above described composition of the inking medium, using differentinking mediums of a substantially identical composition, but in whichthe quantity of cation-type acrylic resin added was varied to provide adiffering viscosity, the relationship among the viscosity of each inkingmedium, the degree of variability of the size of droplets of therespective inking medium and the relative emission output of thefluorescent ink deposit formed by the use of the respective inkingmedium was examined, a result of which is shown in FIG. 5.

As can readily be understood from FIG. 5, when the viscosity of theinking medium for use with the ink jet printer is within the range of 2to 25 cps and preferably within the range of 10 to 20 cps, the degree ofvariability of the ink droplet size is smaller than 10% indicating thatthe ink droplets of a substantially uniform size could be obtainedsufficient to result in an excellent printability and, also, asufficient emission output could be obtained.

In the above described composition of the inking medium, using differentinking mediums of a substantially identical composition, but in whichthe quantity of ethanol added was varied to provide a differing surfacetension, the relationship between the surface tension of each inkingmedium and the degree of variability of the size of droplets of therespective inking medium was examined, a result of which is shown inFIG. 6.

As can readily be understood from FIG. 6, when the surface tension ofthe inking medium for use with the ink jet printer is within the rangeof 23 to 4-dyne/cm and preferably within the range of 26 to 37 dyne/cm,the degree of variability of the size of the ink droplets is small andthe ink droplets of a uniform size required by the ink jet printer couldbe obtained accompanied by an excellent printability.

In the above described composition of the inking medium, using differentinking mediums of a substantially identical composition, but in whichthe quantity of the electrolyte (KCI) added was varied to provide adiffering specific resistance, the relationship between the specificresistance of each inking medium and the degree of variability of thesize of droplets of the respective inking medium was examined, a resultof which is shown in FIG. 7.

As can readily be understood from FIG. 7, when the specific resistanceof the inking medium for use with the ink jet printer is equal to orlower than 2,000 Ω·cm and preferably equal to or lower than 1,500 Ω·cm,the degree of variability of the size of the ink droplets is small andthe ink droplets of a uniform size required by the ink jet printer couldbe obtained accompanied by an excellent printability. It is, however, tobe noted that if the specific resistance of the inking medium for usewith the ink jet printer exceeds 2,000 Ω·cm, and if the ink jet printeris particularly of a charged deflection printing system, control ofdeflection of the ink droplets will become difficult to accomplish,resulting in a reduction in print quality with flaws and/or skewsappearing in the printed characters.

In the above described composition of the inking medium, using differentinking mediums of a substantially identical composition, but in whichKOH was added in addition to KCL and the quantity of KOH added wasvaried to provide a differing pH value, the relationship between the pHvalue and the dispersion stability of the respective inking medium wasexamined, a result of which is shown in FIG. 8. It is to be noted thatthe dispersion stability is expressed in terms of the percentage of asupernatant liquid relative to the total amount of the respective inkingmedium, which supernatant liquid was obtained after the respectiveinking medium had been allowed to stand for one week.

As can readily be understood from FIG. 8, when the pH value of theinking medium is within the range of 4.5 to 10 and preferably within therange of 5 to 7, both the dispersibility and the dispersion stability ofthe inking medium are extremely satisfactory. It is, however, to benoted that if the pH value of the inking medium for use with the ink jetprinter is smaller than 4.5 or greater than 10, the dyes used in theinking medium tend to coagulate.

Thus, when the inking medium of the present invention for use with anink jet printer is prepared to a viscosity within the range of 2 to 25cps, a surface tension within the range of 23 to 40 dyne/cm, a specificresistance not higher than 2,000 Ω·cm and a pH value within the range of4.5 to 10, the inking medium excellent in dispersion stability,substantially free from ink run, excellent in printability and high inemission output can be obtained.

Fluorescent Composition 2

The fluorescent substance of the present invention comprises a salt ofoxyacid containing one or more elements selected from the groupconsisting of Nd, Yb and Er. While specific examples of this salt ofoxyacid include vanadate, phosphate, borate, molybdate and tungstate,the use of the phosphate compound is recommended because of itsexcellent chemical resistance.

More specifically, this fluorescent substance comprises phosphate havingone of the following general chemical formulas:

Ln_(X)A_(1−X)PO₄  (1)

wherein Ln represents at least one element selected from the groupconsisting of Nd, Yb and Er, A represents at least one element selectedfrom the group consisting of Y, La, Gd, Bi, Ce, Lu, In and Tb, and Xrepresents a value within the range of 0.01 to 0.99.

DE_(1−X)Ln_(X)P_(Y)O_(Z)  (2)

wherein D represents at least one element selected from the groupconsisting of Li, Na, K, Rb and Cs, E represents at least one elementselected from the group consisting of Y, La, Gd, Bi, Ce, Lu, In and Tb,Ln represents at least one element selected from the group consisting ofNd, Yb and Er, X represents a value within the range of 0.01 to 0.99, Yrepresents a value within the range of 1 to 5, and Z represents a valuewithin the range of 4 to 14. It is, however, to be noted that theelement D in the general chemical formula (2) may not necessarily beemployed.

Specific examples of charge stocks used to prepare the fluorescentsubstances are shown in FIGS. 9 and 10 wherein Samples 1 to 14 pertainsto the present invention while Sample 15 pertains to a comparison, andthe calcinating temperature at which each composition shown in FIGS. 9and 10 was calcinated and the composition of each of the resultantinfrared-excitable fluorescent substances are shown in FIGS. 11 and 12together with their particle size.

The charge stocks for each of Samples 1 to 15 shown in FIGS. 9 and 10were, after having been calcinated at the temperature specified in FIGS.11 and 12 for each Sample, treated with a hot water and 1 mole of nitricacid to remove non-reacted materials to thereby provide the respectiveinfrared-excitable fluorescent substance.

As FIGS. 11 and 12 make it clear, the fluorescent substances obtainedaccording to the embodiment of the present invention have a particlesize of not greater than 4 μm which is smaller than the particle size (6μm) of the fluorescent substance according to the comparison. Inparticular, some of the fluorescent substances according to theembodiment of the present invention has a particle size not greater than1 μm and which is smaller than the wavelength of the maximum intensityof the exciting light and that of the maximum intensity of thefluorescent light.

Observation of the fluorescent particles with the use of a scanningelectron microscope has indicated that the shape and size of thefluorescent particles were substantially uniform, representing noacicular shape, but a shape similar to stones on a river-shore.

Emission spectra of Samples 1 and 7 according to the embodiment of thepresent invention and of Sample 15 according to the comparison are shownin FIGS. 13, 14 and 14, respectively. As shown in FIG. 13, Sample 1having an average particle size of 0.6 μm has exhibited the wavelengthof the fluorescent light which is 0.98 μm (980 nm) in response to thewavelength of 0.81 μm (810 nm) of the exciting light. Thus, the averageparticle size of Sample 1 is extremely smaller than the wavelength ofboth of the exciting light and the fluorescent light. Similarly, FIG. 14makes it clear that the average particle size of Sample 7, which is 1.0μm, is extremely smaller than the wavelength of both of the excitinglight and the fluorescent light emitted thereby.

Other constituents of the fluorescent composition, such as, for example,binder and solvent, than that shown may be identical with thosepreviously discussed in connection with the Fluorescent Composition 1,and therefore they are not reiterated for the sake of brevity.

Fluorescent Composition 3

The fluorescent substance containing Fe and Er, both as an opticalactive element, and at least one element selected from the groupconsisting of Sc, Ga, Al, In, Y, Bi, Ce, Gd, Lu and La is used.

More specifically, this fluorescent substance is an infrared-excitablefluorescent substance having one of the following general chemicalformulas:

G₃J₅O₁₂  (3)

GJO₃  (4)

G₂J₄O₁₂  (5)

wherein G represents Er and at least one element selected from the groupconsisting of Y, Bi, Ce, Gd, Lu and La and J represents Fe and at leastone element selected from the group consisting of Sc, Ga, Al and In.

The respective fluorescent substance having one of the above generalchemical formulas is in practice employed alone or in the form of amixture.

Specific examples of the infrared-excitable fluorescent substanceinclude those expressed by the following chemical formulas:

a. Er_(0.2)Y_(2.8)Fe_(1.5)Al_(3.5)O₁₂

b. Er_(0.5)Y_(2.5)Fe_(1.5)Ga_(3.5)O₁₂

c. Er_(0.2)Lu_(2.8)Fe_(2.5)Al_(3.5)O₁₂

d. Er_(0.05)La_(0.95)Fe_(0.3)Al_(0.7)O₃

e. Er_(0.02)Lao_(0.98)Fe_(0.1)Ga_(0.9)O₃

A method of preparing these fluorescent substances will now bedescribed.

After charge stocks of a quantity shown in terms of gram in FIG. 16 hadbeen sufficiently mixed in a mortar, the charge stocks were calcinatedat the respective temperature specified in FIG. 16 and then treated witha hot water and 2 moles of nitric acid to remove non-reacted materialsto thereby provide the respective infrared-excitable fluorescentsubstances which are identified by Samples 16 to 20 in FIG. 16.

An emission spectrum of Sample 16, that is, (ErY)₃(FeAl)₅O₁₂, is shownin FIG. 17. A spectral sensitivity characteristic of a Ge photodiode isshown in FIG. 18 and a spectral sensitivity characteristic of an InGaAsphotodiode is shown in FIG. 19.

Since while as shown in FIG. 17 the emission spectrum of the fluorescentsubstance containing Er exhibits a peak value at about 1,540 nm, the Gephotodiode and the InGaAs photodiode have a high sensitivity at awavelength within the range of 1,400 to 1,600 as shown in FIGS. 18 and19, respectively, these photodiode can be advantageously employed as alight receiving element for the purpose of the present invention and theuse thereof is specifically advantageous in that a fine fluorescent marksuch as a pattern of code bars can be accurately and assuredly read outeven though a high reading speed is employed.

It is, however, to be noted that other than those photodiodes discussedabove, any one of a PbS photodiode (sensitive to light of about 600 to1,800 nm) and a PbSe photodiode (sensitive to light of 1,000 to 4,500nm) may be equally employed.

The absorption and emission spectrum characteristics discussed above canbe equally exhibited even with the other infrared-excitable fluorescentsubstances containing Fe or Er.

Fluorescent Composition 4

The fluorescent substance containing Yb as an optical active element,and at least one element selected from the group consisting of Sc, Ga,Al, In, Y, Bi, Ce, Gd, Lu and La is used.

More specifically, this fluorescent substance is an infrared-excitablefluorescent substance having one of the following general chemicalformulas:

L₃M₅O₁₂  (6)

LMO₃  (7)

L₂M₄O₁₂  (8)

wherein L represents Yb and at least one element selected from the groupconsisting of Y, Bi, Ce, Gd, Lu and La and M represents Fe and at leastone element selected from the group consisting of Sc, Ga, Al and In.

The respective fluorescent substance having one of the above generalchemical formulas is in practice employed alone or in the form of amixture.

Specific examples of the infrared-excitable fluorescent substanceinclude those expressed by the following chemical formulas:

a. Yb_(0.3)Y_(2.7)Al₅O₁₂ (Sample 21) b.Yb_(0.2)Gd_(2.5)Ga_(0.5)Al_(4.5)O₁₂ (Sample 22) c. Yb_(0.4)Y_(2.6)Ga₅O₁₂(Sample 23) d. Yb_(0.1)La_(0.95)AlO₃ (Sample 24) e.Yb_(0.05)La_(0.95)Ga_(0.1)Al_(0.9)O₃ (Sample 25)

After charge stocks of a quantity shown in terms of gram in FIG. 20 hadbeen sufficiently mixed in a mortar, the charge stocks were calcinatedat the respective temperature specified and then treated with a hotwater and 2 moles of nitric acid to remove non-reacted materials tothereby provide the respective infrared-excitable fluorescent substanceswhich are identified by Samples 21 to 25 identified in FIG. 20.

An absorption spectrum of Sample 21, that is, Yb_(0.3)Y_(2.7)Al₅O₁₂, isshown in FIG. 21.

As this figure makes it clear, this fluorescent substance exhibits apeak absorption spectrum at a wavelength of about 910 to about 950 nm.Therefore, if irradiated by the exciting light of a wavelength withinsuch range, such fluorescent substance emits a fluorescent light havinga peak value of about 1,030 nm.

FIG. 22 illustrates a change in intensity of the fluorescent lightemitted by the fluorescent substance, Yb_(X)Y_(1−X)Al₅O₁₂, which tookplace when the molar ratio X of Yb contained in such fluorescentsubstance was varied.

As FIG. 22 makes it clear, when the molar ratio of Yb in the fluorescentsubstance, Yb_(X)Y_(1−X)Al₅O₁₂, exceeds 0.7, the emission intensity ofthe fluorescent light lowers. Therefore, it is clear that if the molarratio X of Yb is chosen to be within the range of 0.05 to 0.7,preferably within the range of 0.1 to 0.5 and more preferably within therange of 0.2 to 0.45, the emission intensity of the fluorescent light ishigh.

Observation of the particles of Yb_(X)Y_(1−X)Al₅O₁₂ with the use of ascanning electron microscope has indicated that they have generallysmooth surfaces with no substantial surface irregularity and of agenerally uniform size, neither extremely big nor extremely small, andof a generally round shape similar to a shape of a fruit. Thefluorescent particles of a particle size within the range of 1 to 3 μmoccupy 60 wt % or more (or about 80 wt %) of the fluorescent particlesrelative to the total weight thereof, and an average shape ratio (theratio of the minor axis relative to the major axis) of the fluorescentparticles is not greater than 2.0, most of them being round in shapewith no acicular particle sufficient to exhibit a satisfactorydispersibility in the binder used.

Fluorescent Composition 5

The fluorescent substance comprising a rare earth element containingorganic material containing at least one rare earth element selectedfrom the group consisting of Nd, Yb or Er and carrying an organicmaterial capable of absorbing infrared rays of light of 700 to 1,000 nmis used.

The organic material referred to above may be one or more organicmaterials selected from the group consisting of polymethine,anthraquinone, dithiol metal, phthalocyanine, indophenol and azo dyes.

More specifically, the polymethine dyestuff referred to above includes,for example, “IR-125”, “IR-140” (available from Kodak LaboratoriesChemicals) or “IR-820B” (available from Nippon Kayaku Kabushiki Kaisha).The anthraquinone dyestuff referred to above includes, for example, “IR750” (available from Nippon Kayaku Kabushiki Kaisha). The dithoile metaldyestuff referred to above includes, for example, “Tetrabutylphosphonium-bis-(1,2-benzene chiolite) nicolayite (III)” available fromMitsui Toatsu Kabushiki Kaisha. The phthalocyanine dyestuff includes,for example, Zn-naphthalocyanine or the like. In addition of thesedyestuff, indophenol and azo dyestuff may also be used. Of them the useof the products identified by “IR 125”, “IR 140”, “IR 750” or “IR 820B”are preferred because they exhibit an emission intensity which is highfor unitary weight thereof.

The reason that when the organic material capable of absorbing theinfrared rays of light is carried on the rare earth element, theemission intensity during a high speed reading can be increased to avalue higher than that exhibited by the rare earth element alone appearsto be as follows.

Namely, during a process in which energies absorbed by the organicmaterial capable of absorbing the infrared rays of light are returned toa ground state, the energies are transferred to the organic materialcontaining at least one rare earth element selected from the groupconsisting of Nd, Yb and Er to thereby sensitize the fluorescing actionof the rare earth element.

The fluorescent substance that can carry the organic material having asensitizing capability should contain at least one rare earth elementselected from the group consisting of Nd, Yb and Er and would not poseany problem if it is added optionally with one or more other elements.

The organic material containing the rare earth element selected from thegroup consisting of Nd, Yb and Er may be of any type provided that itforms a complex or salt with the rare earth element. Examples of theminclude organic carboxylic acids such as benzoic acid, anise acid,toluic acid, cinnamic acid and lauric acid, β-diketones such asbenzotrifluoroacetone and thenoyltrifluoroacetone and cyclic ethers suchas 15-crown-5 and 18-crown-6.

Of them, most of the organic materials to be carried have an aromaticring or a heterocycle and, if the organic material of the organicmaterial containing tone or more rare earth elements selected from thegroup consisting of Nd, Yb and Er is aromatic carboxylic acid,interaction between such organic material and the rare earth element orelements selected from the group consisting of Nd, Yb and Er will bestrengthened to increase the capability to carry.

Although a method of synthesizing the organic material containing therare earth element may not be limited to a specific one, synthesis ofthe aromatic carboxylic acid containing at least one rare earth elementselected from the group consisting of Nd, Yb and Er can be accomplishedby the use of the ion-exchange reaction in the aqueous solution such asreported by M. D. Taylor, supra, or the elimination reaction ofisopropoxide in a non-polarity solvent such as reported by P. N. Kapoor,supra.

The quantity of the organic material containing the rare earth elementor elements selected from the group consisting of Nd, Yb and Er, that iscontained in the organic material capable of absorbing the infrared raysof light may be of any desired value, but preferably within the range of0.001 to 10 wt %. If the content of the organic material is smaller thanthe lowermost limit of 0.001 wt %, the absorption of the exciting lightwill be lowered to such an extent as to result in reduced emission ofthe fluorescent light from the organic material containing the rareearth element or elements. On the other hand, if the content of theorganic material is greater than the uppermost limit of 10 wt %, theconcentration of the organic material capable of absorbing the infraredrays of light will increase resulting in energy exchange between theorganic materials and, consequently, the emission of the fluorescentlight from the organic material containing the rare earth element orelements will be lowered.

Where the infrared-excitable fluorescent substance carrying this organicmaterial is used as an inking medium, any type of commercially availablebinder may be employed, but the use of polyvinyl alcohol (PVA) or anacrylic resin is preferred for the binder because of the carryingcapability of the organic material.

If desired, a solvent may be employed. Examples of the solvent that canbe used include water, alcohol, ketone, ester, ether, aromatichydrocarbon and fatty hydrocarbon or a mixture thereof.

Depending on the printing method in which the infrared-excitablefluorescent inking composition is used, one or more of a dispersant, adefoaming agent, a surface active agent, a humectant and a chargeimparting agent may be employed. Also, if desired, any colorconditioning dye and/or a fluorescent dye may be employed.

Hereinafter, the fluorescent substance of the present invention will beillustrated by way of examples.

EXAMPLE 1

1 part by weight of complex salt of cinnamic acid with neodymium andytterbium was suspended in 20 parts by weight of water and was then,while being stirred, added dropwise with a solution prepared bydissolving 0.005 part by weight of anthraquinone dyestuff (“IR 750”available from Nippon Kayaku Kabushiki Kaisha. Absorption peak at 750nm) into 1 part by weight of DMF. After one hour stirring, the mixturewas filtered and dried to obtain the infrared-excitable fluorescentsubstance.

EXAMPLE 2

1 part by weight of complex salt of cinnamic acid with neodymium andytterbium was suspended in 20 parts by weight of water and was then,while being stirred, added dropwise with a solution prepared bydissolving 0.003 part by weight of polymethine dyestuff (“IR-820B”available from Nippon Kayaku Kabushiki Kaisha. Absorption peak at 820nm) into 1 part by weight of DMF. After one hour stirring, the mixturewas filtered and dried to obtain the infrared-excitable fluorescentsubstance.

EXAMPLE 3

1 part by weight of ytterbium benzoate was suspended in 20 parts byweight of water and was then, while being stirred, added dropwise with asolution prepared by dissolving 0.003 part by weight of polymethinedyestuff (“IR-820B” available from Nippon Kayaku Kabushiki Kaisha.Absorption peak at 820 nm) into 1 part by weight of DMF. After one hourstirring, the mixture was filtered and dried to obtain theinfrared-excitable fluorescent substance.

Comparison 1

The infrared-excitable fluorescent substance was prepared by pulverizingLiNd_(0.5)Yb_(0.5)P₄O₁₂ with the use of a ball mill.

Comparison 2

The infrared-excitable fluorescent substance was obtained in a mannersimilar to Example 1, except that the anthraquinone dye (“IR 750) usedin Example 1 was not employed.

(High Speed Reading Test)

Each of the infrared-excitable fluorescent substances obtained underExamples 1 to 3 and Comparisons 1 and 2 was molded into a respectivedisc test-piece of 5 mm in diameter and 2 mm in thickness. A high speedreading test was carried out by scanning the testpiece at a speed of 8m/sec, irradiating the testpiece by means of a commercially availableGaAlAs light emitting diode and detecting the fluorescent light by meansof a Si—PIN photodetector capable of detecting light of 970 nm. Theexciting light emitted from the GaAIAs light emitting diode was of awavelength varying depending on the exciting wavelength of the organicmaterial (the wavelength of the exciting light required for the organicmaterial to emit fluorescent light) so far as the respective fluorescentsubstances of Examples 1 to 3 are concerned. An optical filter (“IR-94”available from Fuji Photo Film Co., Ltd.) was placed in front of thephotodetector. The result of the high speed reading test conducted oneach of those fluorescent substances is shown in Table 1 below.

TABLE 1 Exciting Relative Wavelength (nm) Intensity (%) Example 1 760700 Example 2 800 650 Example 3 760 800 Comp. 1 800 Failed Comp. 2 800100

Using the specific fluorescent substance and the specific binder, afluorescent inking medium was prepared in the following manner.

EXAMPLE 4

complex salt of cinnamic acid with neodymium and ytterbium parts byweight Anthraquinone dyestuff (IR 750) 0.005 part by weight PVA 4 partsby weight Water/EtOH (812) 20 parts by weight

This composition was dispersed for 24 hours in a ball mill to providethe inking medium which was subsequently loaded in an ink jet printer tofor a fluorescent mark.

Comparison 3

A fluorescent mark was formed in a manner similar to Example 4, exceptthat the complex salt of cinnamic acid with neodymium and ytterbium usedin Example 4 was not used.

Comparison 4

A fluorescent mark was formed in a manner similar to Example 4, exceptthat the anthraquinone dyestuff (IR 750) used in Example 4 was not used.However, in Table 2 below, the fluorescent mark irradiated by theexciting wavelength of 760 nm and the fluorescent mark irradiated by theexciting wavelength of 800 nm are identified by (a) and (b),respectively.

EXAMPLE 5

Ytterbium cinnamate 1 parts by weight Polymethine dyestuff (IR 820)0.003 part by weight PVA 4 parts by weight Water/EtOH (8/2) 20 parts byweight

This composition was dispersed for 24 hours in a ball mill to providethe inking medium which was subsequently loaded in an ink jet printer tofor a fluorescent mark.

Comparison 5

A fluorescent mark was formed in a manner similar to Example 5, exceptthat the polymethine dyestuff (IR 820) used in Example 5 was not used.

Comparison 6

A fluorescent mark was formed in a manner similar to Example 5, exceptthat the ytterbium cinnamate used in Example 5 was not used.

EXAMPLE 6

Ytterbium benzoate 1 parts by weight Polymethine dyestuff (IR 820) 0.005part by weight PVA 4 parts by weight Water/EtOH (8/2) 20 parts by weight

This composition was dispersed for 24 hours in a ball mill to providethe inking medium which was subsequently loaded in an ink jet printer tofor a fluorescent mark.

Comparison 7

A fluorescent mark was formed in a manner similar to Example 6, exceptthat the polymethine dyestuff (IR 820) used in Example 6 was not used.

Comparison 8

A fluorescent mark was formed in a manner similar to Example 6, exceptthat the ytterbium benzoate used in Example 6 was not used.

(High Speed Reading Test)

Printed matter prepared by the use of each of the infrared-excitablefluorescent substances obtained under Examples 4 to 6 and Comparisons 3to 7 was subjected to a high speed reading test. This high speed readingtest was carried out by scanning the testpiece at a speed of 8 m/sec,irradiating the testpiece by means of a commercially available GaAlAslight emitting diode and detecting the fluorescent light by means of aSi—PIN photodetector capable of detecting light of 970 nm. The excitinglight emitted from the GaAIAs light emitting diode was of a wavelengthvarying depending on the exciting wavelength of the organic material sofar as the printed matters under Examples 4 to 6 and Comparisons 3, 6and 8 are concerned. An optical filter (“IR-94” available from FujiPhoto Film Co., Ltd.) was placed in front of the photodetector. Theresult of the high speed reading test conducted on each of those printedmatters is shown in Table 1 below.

TABLE 2 Exciting Relative Wavelength (nm) Intensity (%) Example 4 760100 Example 5 800 100 Example 6 800 129 Comp. 3 760 30 Comp. 4 (a) 760Failed Comp. 4 (a) 800 40 Comp. 5 800 20 Comp. 6 800 10 Comp. 7 800 10Comp. 8 800 40

As Tables 1 and 2 make it clear, the fluorescent substance obtainedunder each of Examples 1 to 3 results in a sufficient emission outputduring the high speed reading as compared with that under each ofComparisons 1 and 2. Also, the fluorescent substance obtained under eachof Examples 1 to 3 can be excited to emit a fluorescent light inresponse to a varying exciting wavelength.

The inking medium obtained under each of Examples 4 to 6 is suited foruse with the ink jet printer.

Fluorescent Composition 6

The water-resistance of the fluorescent substance was increased byemploying, as a matrix material, a salt prepared from at least one of Ndand Yb as an optical active element, an oxide of at least one of Mo andW and an alkaline earth metal.

Preferably, the atomic ratio s of the optical active element relative tothe oxide of at least one of Mo and W is greater than 0, but equal to orsmaller than 2, and the atomic ratio t of the alkaline earth metalrelative to such oxide is greater than 0, but equal to or smaller than3.

More specifically, the fluorescent substance having an increased waterresistance is a compound of the following general formula (9):

(Nd_(1−X)Yb_(X))_(Y)Q_(Z)(RO₄)  (9)

wherein Q represents at least one element selected from the groupconsisting of Ca, Mg, Sr and Ba, R represents at least one elementselected from the group consisting of Mo and W, X represents a valuewithin the range of 0 to 1, Y represents a value greater than 0, butsmaller than 1, and Z represents a value greater than 0, but smallerthan 1.

Alternatively, the fluorescent substance is a compound of the followinggeneral formula (10):

(Nd_(1−X)Yb_(X))_(2Y)Q_(8−3Y)(RO₄)₈  (10)

wherein Q represents at least one element selected from the groupconsisting of Ca, Mg, Sr and Ba, R represents at least one elementselected from the group consisting of Mo and W, X represents a valuewithin the range of 0 to 1 and Y represents a value greater than 0, butequal to or smaller than 8/3.

It is to be noted that X and Y are preferred to be 0.02≦X≦0.6 and1/3≦Y≦5/3, respectively. If X is smaller than 0.02, the concentration ofYb which is the emission center responsible for the emission will belowered, and on the other hand, if X is greater than 0.6, theconcentration of Nd which is a sensitizer for absorbing the excitinglight will be lowered, both resulting in possible reduction in emissionintensity. Also, if Y is smaller than 1/3, the concentration of Nd andYb serving as an optical active element will be lowered, and on theother hand, if Y is greater than 5/3, the concentration of Nd and Ybwill be increased to such an extent as to result in a concentrationquenching, which in turn results in possible reduction in emissionintensity.

Although examples of the alkaline earth metal include Ca, Mg, Sr and Ba,the use of Ca is particularly preferred. The content of the alkalineearth metal is preferred to be equal to or lower than 10 atomic percent.Also, for R in the formulas, Mo is preferred.

When this fluorescent substance is to be prepared, at least one opticalactive element of Nd or Yb, at least one oxide of Mo or W and thealkaline earth metal should be mixed together and then added to a fluxmaterial containing a salt expressed by T₂RO₄.nH₂O (wherein T representsat least one element selected from the group consisting of Li, Na and K,R represents at least one element selected from the group consisting ofMo and W, and n represents numerical value equal to or greater than 0),followed by calcination. After the calcination, the fluorescentparticles can be rendered extremely fine by dissolving the calcinatedproduct with the use of a solvent to remove the flux material.

In the composition of the flux material, the use of Na and Mo for T andR is particularly preferred. The mixing molar ratio of the flux materialrelative to the fluorescent material is preferably equal to or greaterthan 1, but not greater than 10. If this molar ratio is smaller than 1,the flux material will not exhibit a satisfactory effect and theparticles of the infrared-excitable fluorescent substance can hardly bedivided into microparticles. On the other hand, if the molar ratioexceeds 10, the preparation would require an increased amount ofmaterial cost and the use of a bulky crucible, resulting in increasedcost of manufacture.

The fluorescent substance so prepared is in the form of supermicroparticles of an average particle size not greater than 1 μm and issuited for use in the practice of a printing technique such as an inkjet printer and an ink ribbon.

This fluorescent substance is characterized in that the length of timerequired for the resultant fluorescent afterglow, subsequent tointerruption of irradiation of the exciting light, to attain 10% of theemission output is within 500 μsec, and is therefor suited for use in afluorescent detecting system in which the fluorescent light emitted bythe irradiation of the exciting light of a pulsating period of 1 msec isidentified or the fluorescent light emitted is identified at a run speedof not lower than 0.5 m/sec.

This fluorescent substance has an excellent water resistance as itswater solubility exhibited when it is immersed in water for 20 hours isnot higher than 2 wt %.

When an inking medium prepared by dispersing this fluorescent substancein a transparent binder for dispersing and retaining the fluorescentparticles is coated on a length of tape, a thermally transferable inkribbon can be obtained. Alternatively, such inking medium can be usedwith an ink jet printer. Since this fluorescent substance has anexcellent water-resistance, it can be used as a paint.

The binder referred to above may be wax, a copolymer of polyvinylchloride and vinyl acetate, a copolymer of ethylene and vinyl acetate,polyester resin, polyurethane resin or polycarbonate resin. If desired,a suitable plasticizer and/or a surface active agent may be addedsuitably.

According to the result of experiments conducted by the inventors inwhich, where anions of the matrix material are, for example, MoO₄ ²⁻,comparison in water solubility was made between the conventionalfluorescent substance in which the rare earth element is added to thematrix material, Na₂MoO₄, having cations in the form of Na⁺ (an alkalinemetal) and the fluorescent substance of the present invention in whichthe rare earth metal is added to the matrix material, CaMoO₄, havingcations in the form of Ca²⁺ (an alkaline metal), the fluorescentsubstance of the present invention did not dissolve even though immersedin water for 500 hours whereas the conventional fluorescent substanceexhibited that about 10 wt % thereof dissolved when immersed in waterfor only 20 hours. Thus, the fluorescent substance of the presentinvention has a superior water resistance.

Specific examples will now be described.

(1) Preparation of Powdery Material

10 kinds of fluorescent substances were prepared in a manner as setforth under the following examples and comparisons and were tested todetermine the shape of fluorescent particles, the average particle sizethereof, the emission wavelength (the wavelength of the fluorescentlight emitted in response to the exciting light), the length of time theafterglow persisted until the intensity of the fluorescent lightattained 10% of the maximum intensity thereof, and the yield (expressedin terms of percent) based on the weight of the fluorescent substancewhich was measured after 100 parts by weight of the fluorescentsubstance was immersed in water for 500 hours and then dried. Results ofcomparison are shown in Table 3.

EXAMPLE 7

0.9 mole of Nd₂O₃, 1 mole of Yb₂O₃, 5 moles of CaCO₃ and 8 moles of MoO₃were sufficiently mixed and pulverized to give a powdery mixture whichwas subsequently filled in a crucible. This crucible containing thepowdery mixture was heated in an electric furnace to 750° C. at a rateof about 180° C./hr to calcinate the powdery mixture at 750° C. for 2hours. After the calcination, the powdery mixture was cooled andpulverized in a mortar to provide the fluorescent substance which isNd_(1.8)Yb_(0.2)Ca₅(MoO₄)₈.

EXAMPLE 8

0.9 mole of Nd₂O₃, 0.1 mole of Yb₂O₃, 21 moles of CaCO₃ and 24 moles ofMoO₃ were sufficiently mixed and pulverized to give a powdery mixturewhich was subsequently filled in a crucible. This crucible containingthe powdery mixture was heated in an electric furnace to 750° C. at arate of about 180° C./hr to calcinate the powdery mixture at 750° C. for2 hours. After the calcination, the powdery mixture was cooled andpulverized in a mortar to provide the fluorescent substance which isNd_(1.8)Yb_(0.2)Ca₂₁(MoO₄)₂₄.

EXAMPLE 9

4.5 moles of Nd₂O₃, 0.5 mole of Yb₂O₃, 9 moles of CaCO₃ and 24 moles ofMoO₃ were sufficiently mixed and pulverized to give a powdery mixturewhich was subsequently filled in a crucible. This crucible containingthe powdery mixture was heated in an electric furnace to 750° C. at arate of about 180° C./hr to calcinate the powdery mixture at 750° C. for2 hours. After the calcination, the powdery mixture was cooled andpulverized in a mortar to provide the fluorescent substance which isNd₉YbCa₉(MoO₄)₂₄.

EXAMPLE 10

4.5 moles of Nd₂O₃, 0.5 mole of Yb₂O₃, 9 moles of CaCO₃ and 24 moles ofWO₃ were sufficiently mixed and pulverized to give a powdery mixturewhich was subsequently filled in a crucible. This crucible containingthe powdery mixture was heated in an electric furnace to 1,000° C. at arate of about 250° C./hr to calcinate the powdery mixture at 1,000° C.for 2 hours. After the calcination, the powdery mixture was cooled andpulverized in a mortar to provide the fluorescent substance which isNd₉YbCa₉(WO₄)₂₄.

EXAMPLE 11

1 mole of Nd₂O₃, 21 moles of CaCO₃ and 24 moles of MoO₃ weresufficiently mixed and pulverized to give a powdery mixture which wassubsequently filled in a crucible. This crucible containing the powderymixture was heated in an electric furnace to 750° C. at a rate of about180° C./hr to calcinate the powdery mixture at 750° C. for 2 hours.After the calcination, the powdery mixture was cooled and pulverized ina mortar to provide the fluorescent substance which is Nd₂Ca₂₁(MoO₄)₂₄.

EXAMPLE 12

0.9 mole of Nd₂O₃, 0.1 mole of Yb₂O₃, 5 moles of CaCO₃ and 8 moles ofMoO₃ were mixed, in a molar mixing ratio of 1:8, with a powdery fluxmaterial which is Na₂MoO₄.2H₂O. The mixture was sufficiently mixed andpulverized to give a powdery mixture which was subsequently filled in acrucible. This crucible containing the powdery mixture was heated in anelectric furnace to 750° C. at a rate of about 180° C./hr to calcinatethe powdery mixture at 750° C. for 2 hours. After the calcination, thecalcinated powdery mixture was cooled and ultrasonically flushed in purewater for 1 hour to remove the flux material, followed by drying at 120°C. for 2 hours to thereby provide the fluorescent substance which isNd_(1.8)Yb_(0.2)Ca₅(MoO₄)₈.

An emission spectrum of this fluorescent substance is shown in FIG. 23,the waveform of a response of this fluorescent substance to thepulse-like exciting light is shown in FIG. 24, and a microscopicobservation of the particle structure of this fluorescent substance isshown in FIG. 25.

EXAMPLE 13

0.9 mole of Nd₂O₃, 0.1 mole of Yb₂O₃, 5 moles of CaCO₃ and 8 moles ofMoO₃ were mixed, in a molar mixing ratio of 1:6, with a powdery fluxmaterial which is Na₂WO₄.2H₂O. The mixture was sufficiently mixed andpulverized to give a powdery mixture which was subsequently filled in acrucible. This crucible containing the powdery mixture was heated in anelectric furnace to 750° C. at a rate of about 180° C./hr to calcinatethe powdery mixture at 750° C. for 2 hours. After the calcination, thecalcinated powdery mixture was cooled and ultrasonically flushed in purewater for 1 hour to remove the flux material, followed by drying at 120°C. for 2 hours to thereby provide the fluorescent substance which isNd_(1.8)Yb_(0.2)Ca₅(MoO₄)₈.

EXAMPLE 14

0.9 mole of Nd₂O₃, 0.1 mole of Yb₂O₃, 5 moles of CaCO₃ and 8 moles ofMoO₃ were mixed, in a molar mixing ratio of 1:6, with a powdery fluxmaterial which is K₂WO₄. The mixture was sufficiently mixed andpulverized to give a powdery mixture which was subsequently filled in acrucible. This crucible containing the powdery mixture was heated in anelectric furnace to 750° C. at a rate of about 180° C./hr to calcinatethe powdery mixture at 750° C. for 2 hours. After the calcination, thecalcinated powdery mixture was cooled and ultrasonically flushed in purewater for 1 hour to remove the flux material, followed by drying at 120°C. for 2 hours to thereby provide the fluorescent substance which isNd_(1.8)Yb_(0.2)Ca₅(MoO₄)₈.

Comparison 9

0.9 mole of Nd₂O₃, 0.1 mole of Yb₂O₃, 5 moles of N₂aCO₃ and 8 moles ofMoO₃ were mixed and sufficiently mixed and pulverized to give a powderymixture which was subsequently filled in a crucible. This cruciblecontaining the powdery mixture was heated in an electric furnace to 650°C. at a rate of about 160° C./hr to calcinate the powdery mixture at650° C. for 2 hours. After the calcination, the calcinated powderymixture was cooled and pulverized in a mortar to provide the fluorescentsubstance which is Nd_(0.9)Yb_(0.1)Na₅(MoO₄)₄.

Comparison 10

0.2 mole of Nd₂O₃, 0.2 mole of Yb₂O₃, 0.6 mole of Y₂O₃ and 12 moles ofLiH₂PO₄ were mixed and sufficiently mixed and pulverized to give apowdery mixture which was subsequently filled in a crucible. Thiscrucible containing the powdery mixture was heated in an electricfurnace for 2 hours at 700° C. After the calcination, the calcinatedpowdery mixture was pickled in the presence of 1N of HNO₃ andsubsequently washed with pure water to provide, after drying, thefluorescent substance which is Nd_(X)Yb_(Y)Y_(1−X−Y)PO₄.

TABLE 3 Ave. Emission Per- Particle Shape of Part. Wave- sistingFluorescent Size length Time Yield Substance (μm) (nm) (μsec) (%)Example 7 Powdery, aggregate 3 980 370 98 Example 8 Powdery, aggregate 2980 500 99 Example 9 Powdery, aggregate 1 980 240 97 Example 10 Powdery,aggregate 4 980 340 97 Example 11 Powdery, aggregate 3 890 & 140 991,060 Example 12 Non-aggregated 0.7 980 310 99 granules Example 13Non-aggregated 0.8 980 360 99 granules Example 14 Non-aggregated 0.7 980360 98 granules Comp. 9 Non-aggregated, 10 980 650 86 polygonal Comp. 10Non-aggregated, 1 980 1,500 98 polygonal

As Table 3 makes it clear, while the conventional fluorescent substanceshas exhibited a low response and is therefore not suited for excitationby the pulse-like exciting light having a short pulse duration and alsofor a high speed reading by means of a high speed scanner, thefluorescent substance of the present invention has exhibited a highresponse and is therefore suited for excitation by the pulse-likeexciting light having even a short pulse duration and also for a highspeed reading by means of a high speed scanner. Moreover, thefluorescent substance of the present invention has a high durabilityand, in particular, Examples 12 to 14 are effective to provide thefluorescent particles of a particle size not greater than 1 μm that issuited for various printing purposes.

Change of the yield of the fluorescent substance under each of Example12 and Comparison 9, obtained when the latter was immersed in purewater, with passage of time is shown in FIG. 26. The yield shown thereinis expressed in terms of percent by weight of the amount of thefluorescent substance recovered after having been dried relative to 100parts by weight of the fluorescent substance immersed in water for apredetermined length of time.

As can readily be understood from FIG. 26, it has been found that whileaccording to Comparison 9, 10 or more % by weight of the fluorescentsubstance has eluted, the fluorescent substance under Example 12 has notbeen eluted substantially, exhibiting a superior water-resistance.

A fluorescent inking medium was prepared by dispersing 75 parts byweight of the fluorescent substance according to Example 12 into atransparent binder which is a mixture of 15 parts by weight of wax, 5parts by weight of polyester and 5 parts by weight of polyurethane. Thefluorescent inking medium so obtained was applied to a length ofpolyethylene terephthalate tape, 50 μm in thickness and 1 cm in width,to provide a thermal transfer ink ribbon having a dry deposit, 5 μm inthickness, of the inking medium over the length thereof.

Using the resultant ink ribbon a bar code indicative of a ten-digitnumber was printed on a carrier which was subsequently transported at aspeed of 0.9 m/sec in a fluorescent afterglow recognizing system whileirradiated by a pulsating infrared beam of 810 nm in wavelength having aperiod of 0.8 msec to excite the bar code. Information represented bythe ten-digit number printed in the form of the bar code on the carriercould be accurately read out.

2. [Method of Printing Fluorescent Composition and Fluorescent MarkCarrier]

For printing the various fluorescent compositions of the presentinvention discussed hereinbefore, an ink jet recording system is suitedfor a high speed printing. The following ink jet recording systems areknown and any of them can be employed in the practice of the presentinvention:

a) An electric field control system in which an electrostatic force ofattraction is used to expel the inking medium through a nozzle.

b) A drop-on-demand system (a pressure pulse system) in which apiezoelectric element is used to produce a pulsating pressure by whichthe inking medium is expelled through a nozzle.

c) A bubble jet system in which the inking medium is heated to producebubbles by which the inking medium is expelled through a nozzle uponburst of the bubbles.

FIG. 27 depicts the electric field control system for the purpose ofillustration of the principle of ink jet recording. According to thiselectric field control system, an indicia such as a mark or character tobe printed is divided into a dot matrix of pixels so that droplets ofthe inking medium can be charged a voltage proportional to the positioninformation represented by each pixel, the ink droplets beingsubsequently expelled towards a recording medium while having beendeflected in an electric field through which they travelled.

The principle of the electric field control system will now be describedwith reference to FIG. 27. The system includes an ink reservoir 1accommodating a quantity of inking medium 2. The inking medium 2 withinthe reservoir 1 is pressurized by a supply pump 3 and is subsequentlyexpelled through a nozzle 5 with its pressure adjusted by a pressureadjusting valve 4 to a predetermined value. The nozzle 5 has anelectrostriction element 6 built therein, which element 6 is oscillatedby a source of oscillation 7 at a predetermined frequency. Ink dropletsare, as they pass through the nozzle 5, shaped to generally round inkdroplets of a predetermined size in synchronism with the frequency ofoscillation of the electrostriction element 6.

A voltage proportional to an information signal to be recorded isapplied to a charge electrode disponed at a location where the inkingmedium is transformed into the ink droplets, so that the amount ofelectric charge built upon the individual ink droplets can be controlledin synchronism with formation of the ink droplets.

As the ink droplets successively travel through a gap between deflectionelectrodes 9 to which a predetermined voltage is applied, the inkdroplets are deflected a distance determined by the amount of electriccharge carried thereby before they are successively deposited onto arecording medium, that is, a mark carrier 10. In this way, a pattern ofdots descriptive of a fluorescent marking of a size determined by themagnitude of deflection of the ink droplets and the relative velocity oftravel of the ink droplets between the nozzle 5 and the carrier 10 isformed on a surface of the mark carrier 10 to thereby complete afluorescent mark carrier 10. On the other hand, some of the ink dropletswhich are not used for printing are, without being deflected, collectedby a gutter 11 and are then recovered into the ink reservoir 1 by meansof a recovery pump 12.

The carrier on which the fluorescent composition is deposited tocomplete the fluorescent mark carrier may be a security, a sales slip,an invoice, a card, a book, a surface of merchandise or any other memberon which ink droplets can deposit.

As a result of examination conducted on the content of the fluorescentparticles in the fluorescent ink deposit (i.e., the amount of thefluorescent particles relative to the total weight of the fluorescentink deposit, it has been found that unless the content of thefluorescent particles is smaller than 1 wt % relative to the weight ofthe fluorescent ink deposit on the carrier, no intended emissionintensity can be obtained. Although increase of the content of thefluorescent particles result in a gradual increase of the emissionintensity, the fluorescent particles would aggregate or overlap denselywith the emission density no longer increasing if the content of thefluorescent particles exceeds 50 wt %. Specifically, if the content ofthe fluorescent particles exceeds 30 wt %, the fluorescent ink depositon the carrier would become noticeable in sight and, particularly wherethe fluorescent particles made up of the inorganic compound of arelatively large particle size, the printability exhibited by the inkjet printer or a screen printing technique would be lowered.

Accordingly, when the content of the fluorescent particles in thefluorescent deposit is controlled to greater than 1 wt %, but smallerthan 30 wt %, a desired emission density can be maintained withoutallowing the fluorescent ink deposit to be noticeable in sight and,therefore, the appearance of the fluorescent mark carrier will not beadversely affected, accompanied by a satisfactory print-ability. Thiscontent is particularly advantageous in the case where the fluorescentparticles used have an average particle size not greater than 4 μm andpreferably not greater than 2 μm discussed hereinbefore.

As a result of studies conducted on the relationship between thethickness of the fluorescent ink deposit and the average particle sizeof the fluorescent particles used, it has been found that, if thethickness of the fluorescent ink deposit is controlled to a valuesmaller than 35 times, or preferably 25 times, the average size of thefluorescent particles, the presence of the fluorescent ink depositforming a fluorescent mark on the carrier would neither substantially befelt to the touch nor become noticeable in sight and, for this reason,the appearance of the fluorescent mark carrier would not be adverselyaffected. Accordingly, in the practice of the present invention, it ispreferred that if the average particle size of the fluorescent particlesis 4 μm or 2 μm, the thickness of the fluorescent ink deposit should benot greater than 140 μm or 70 μm, respectively.

As a result of studies conducted on the light transmission exhibited bythe binder used to disperse and retain the fluorescent particles, it hasbeen found that if the transmittance of the exciting and fluorescentlight is higher than 80%, and preferably 90%, penetration of theexciting light into the fluorescent ink deposit and emission of thefluorescent light outwardly from the fluorescent ink deposit take placeefficiently, exhibiting a relatively high emission output sufficient toaccomplish an assured detection of the fluorescent mark.

The inventors have conducted a series of studies on the surfacecondition of the fluorescent ink deposit. Comparison has been madebetween the emission output exhibited when a paint containing thefluorescent particles of the present invention was applied to a film ofsynthetic resin to form the fluorescent ink deposit and that when thesame paint was applied to a paper to form the fluorescent ink depositand, as a result of the comparison, it has been found that the paperhaving the fluorescent ink deposit thereon exhibited a relatively highemission output.

While visual inspection of the surface condition of the fluorescent inkdeposit formed on the film of synthetic resin has indicated that thesurface of the fluorescent ink deposit was smooth, the fluorescent inkdeposit formed on the paper has shown that the surface thereof containedminute surface irregularities. Because of the presence of the minutesurface irregularities, the exciting light impinging upon thefluorescent ink deposit does not undergo a specular reflection andappeared to have participated in activation of the fluorescent substanceand, therefore, a relatively high emission output would have beenobtained. In particular, where the average particle size of thefluorescent particles is smaller than the fiber diameter of fibrousmaterial forming the paper (for example, if the average particle size isabout 0.2 μm), the efficiency of excitation of the fluorescent substanceis high because the fluorescent particles deposit at a varying angle onsurfaces of fibers intertwined randomly and irregularly.

Where the fluorescent ink deposit is to be formed on an item to bedelivered such as a postal matter or a parcel, or a card such as apre-paid card or a commutation card as will be described later, it isrecommended that the resultant fluorescent deposit will not benoticeable in sight. In order for the fluorescent ink deposit to beunnoticeable in sight, one method to accomplish this i to restrict thethickness of the fluorescent ink deposit, but restriction of theabsorption of visible rays of light is also effective to accomplishthis.

The principal component of the fluorescent ink deposit is a mixture ofthe binder and the fluorescent particles and, therefore, if the binderand the fluorescent particles both having a low absorptivity withrespect to the visible rays of light are used so that the absorptivityof the fluorescent ink deposit eventually formed with respect to thevisible rays of light may be restricted to a value lower than 20% andpreferably lower than 10%, it has been found that the fluorescent inkdeposit can be made substantially colorless and nearly transparent and,therefore, the appearance of the fluorescent mark carrier would not beadversely affected.

With the fluorescent mark carrier according to an embodiment of thepresent invention, the fluorescent ink deposits formed thereon will notbe copied onto a transfer paper or will be copied onto a transfer paperin a manner not noticeable in sight when an attempt is made to make acopy of it and, therefore, there is no possibility that the transferpaper would be stained by images of the fluorescent ink deposits on thefluorescent mark carrier.

A specific example, in which the fluorescent mark containing thefluorescent composition is formed on a postal envelope or a postal cardis shown in FIG. 28.

As shown in FIG. 28, a postal matter 13 such as, for example, a postalenvelope, a postal card or a postal tag attached to a parcel has a frontsurface on which not only is a postal stamp 14 attached, but also a zipcode 15, an address 16 and an addressee 17 are written down. In additionto those items present on the front surface of the postal matter 13, barcode information associated with the address is printed on apredetermined area by the ink jet recording system to form thefluorescent ink deposits 18. Since the bar code information isrepresented by the fluorescent mark not visible under visible rays oflight, the appearance of the postal matter 13 will not be adverselyaffected.

Another example of the postal matter 13 is shown in FIG. 29. In thisexample, the bar code associated with the address is printed on a label19 in the form of the fluorescent mark, which label 19 is, when theaddresser intends to post the postal matter 13, affixed to apredetermined area of the postal matter 13 before the latter issubmitted to a post office. It is to be noted that if the area to whichthe label 19 is to be affixed varies from one postal matter to another,information reading would be hampered and, therefore, the postal matter13 has a blank box printed at that area so that the position where thelabel 19 is to be affixed can be specified.

While reference has been made to the postal matter, a similardescription equally applies to any other matter desired to be deliveredsuch as, for example, a parcel to be delivered by a courier or anin-house mail.

Also, while the information such as the address, the addressee and so onhas been shown as printed with the use of the fluorescent composition,other information such as the address of the sender, the addresser'sname may also be printed.

FIG. 30 illustrates a flowchart explanatory of the process of impartingand reading the bar code information to and from the postal matter 13.

Postal matters 13 collected at a post office are first put into arectifying machine so that the postal matters 13 can be rectified so asto orient in a predetermined direction. Since some of the postal matters13 have a label 19 affixed thereto and the others do not have, thepostal matters 13 are classified by a classifying machine into twogroups, one including the postal matters 13 having no label and theother including the postal matters 13 with labels 19 affixed thereto.This classification can be accomplished by irradiating the predeterminedarea of each postal matter 13 where the label 19 ought to be affixed.Should a fluorescent light from the predetermined area of some of thepostal matters 13 be detected, it is clear that such some of the postalmatters 13 have a label 19 affixed thereto, or otherwise the postalmatters 13 would be deemed having no label 19.

The postal matters 13 having no label 19 affixed thereto are transferedto an optical character recognizing machine (OCR) 22 where the zip code15 and the address 16 are optically read out. Based on the informationread out by the OCR 22, the bar code information associated with theaddress is printed by an ink jet printer (IJP) 23 on the predeterminedarea of each of the postal matters 13.

Both of the postal matters 13 having no label 19 affixed thereto, butthe bar code information printed thereon and the postal matters 13having the labels 19 affixed thereto are subsequently transferred onto abar code sorting machine 24 by which the bar code information isoptically read out so that the postal matters 13 can be subsequentlysorted according to the bar code information.

The bar code sorting machine 24 referred to above may generally comprisean optical reading apparatus for optically reading the bar codeinformation and a sorting apparatus for sorting the postal matters 13according to the bar code information read out by the optical readingapparatus.

Numerous preferred embodiments of the optical reading apparatusaccording to the present invention will now be described individually.

Optical Reading Apparatus: Embodiment 1

FIG. 31 illustrates a schematic structure of the optical readingapparatus 25. This optical reading apparatus 25 broadly includes thereader optics and a reading circuit.

The reader optics is comprised of a semiconductor laser drive circuit26, a semiconductor laser 27, a lens 28, a specular reflecting mirror29, plano-convex lenses 30 and 31, a slit member 32, a filter 33 and aphotodiode 34.

Rays of exciting light 60 emitted from the semiconductor laser 27 isconverged by the lens 28 into a pencil of exciting light of about 1 mmin diameter. This pencil of exciting light subsequently passes throughan aperture 35 of about 2 mm in diameter defined in a central portion ofthe specular reflecting mirror 29, as best shown in FIG. 32, before itis projected on to the postal matter 13, which is an example of thefluorescent mark carrier 10, through the lens 30 in a directionperpendicular to the plane of the postal matter 13.

If the exciting light 60 is projected towards the mirror 29 withoutbeing converged, part of the exciting light 60 will be cut out by aperipheral lip region of the mirror 29 around the aperture 35 and, forthis reason, the quantity of the exciting light (exciting energies)actually reaching the postal matter 13 is substantially reduced to suchan extent as to reduce the emission output and, therefore, it isnecessary to restrict the diameter of a bundle of the exciting light 60to a value smaller than the diameter of the aperture 35. In theillustrated embodiment, in consideration of any possible error whichwould occur in installing the various component parts, the excitinglight 60 is converged into the pencil of exciting light of 1 mm indiameter for the diameter of 2 mm of the aperture 35.

The postal matter 13 is transported in a direction shown by the arrow ata speed of, for example, 4 m/sec and, during the transportation of thepostal matter 13, the fluorescent ink deposits 18 in the form of barsare irradiated by the exciting light to emit a fluorescent light whichthen pass through the first plano-convex lens 30. The fluorescent lightpassing through the plano-convex lens 30 is subsequently reflected bythe mirror 29 so as to pass through the second plano-convex lens 31. Thefluorescent light passing through the second plano-convex lens 31 isconverged thereby and further passes through the slit member 32 and thefilter 33 before it is sensed by the photodiode 34.

The reader circuit referred to above includes a detecting circuit 36having an amplifier and a filter circuit, a digitizer circuit 37, adecoder circuit 38, a serial interface 39 and a personal computer 40 forprocessing data.

While it may be contemplated to use a semitransparent mirror in place ofthe perforated mirror 29, the use of the semitransparent mirror may havea problem in that only substantially half of the fluorescent lightemitted will be reflected towards the photodiode 34 and, therefore, thephotodiode 34 will issue an output which is of a value generally halfthat ought to be when the entire quantity of the fluorescent light isreceived. In the practice of the present invention, in order to increasethe amount of light reflected and to make the bar code information onthe postal matter 13 to be read out accurately and assuredly at a highspeed, the use has been made of a highly reflective mirror 20 having theminute aperture 35 defined therein and also having a reflectance ofhigher than 50%. The perforated mirror 29 may be in the form of aspecular mirror formed by vapor-depositing aluminum on a surface of aglass plate.

The postal matters 13 may have a varying thickness and may oftenfluctuate in a direction parallel to the optical axis of a transportsystem. For this reason, the light having passed through the mirror 29is allowed to impinge upon each postal matter 13 at a substantiallyright angle to the plane of each postal matter 13. By so doing, eventhough the thickness of the postal matter 13 varies and/or fluctuationoccurs in a direction parallel to the optical axis of the transportsystem, the bar code information can be assuredly read out without beingadversely affected thereby.

FIG. 33 illustrates a diagram used to explain the function of the slitmember 32 and how it solves the problem. In the example shown in FIG.33, the slit member 32 is shown to be disposed in front of the firstplano-convex lens 30 and the fluorescent light 61 emitted from thefluorescent ink deposit 18 on the postal matter 13 (i.e., thefluorescent mark carrier 10) passes through the slit 32 a defined in theslit member 32 and is then guided onto the first plano-convex lens 30.

The slit member 32 is so designed and so positioned that, while as shownby the solid line in FIG. 33 the fluorescent light 61 emitted from thefluorescent ink deposit 18 when the latter is aligned with the slit 32 ais received having passed through the slit 32 a, the fluorescent light61 emitted from the fluorescent ink deposit 18 which has been moved pastthe position aligned with the slit 32 a as a result of the continuedtransport of the postal matter 13 (i.e., the fluorescent mark carrier10), as shown by the phantom line, can be cut off by the slit member 32.Since in this way only the fluorescent light 61 emitted from thefluorescent ink deposit 18 then aligned with the slit 32 a is selected,the slit member 32 is disposed so adjacent to a transport means 62 forthe postal matters 13 (i.e., the fluorescent mark carriers 10) aspossible.

It may occur that when the postal matter 13 having a substantialthickness is transported to a reading station, transport of the postalmatter 13 may be halted with the front of the postal matter 13 abuttedagainst the slit member 32 and/or the slit member 32 may be damaged incontact therewith.

For this reason, as shown in FIG. 31, the slit member 32 is eliminatedout of the path of transport of the postal matters 13 and is placedbetween the second plano-convex lens 31 and the light receiving element34. By so doing, a relatively large space can be secured between thetransport means 62 and the first plano-convex lens 30 sufficient toallow the postal matter 13 of a substantial thickness to pass while theslit member 31 serves its intrinsic function.

FIGS. 34 and 35 are schematic diagrams used to explain the relationshipbetween the pattern of laser irradiation emitted from the semiconductorlaser and the pattern of bar codes. As best shown in FIG. 34, thesemiconductor chip 41 is of a laminated structure including an AIelectrode 42, a p-type electrode 43, a p-type GaAs substrate 44, acurrent trapping layer 45 made of n-type GaAs, a clad layer 46 made ofn-type Ga_(1−X)Al_(X)As, an active layer 47 made of p-typeGa_(1−Y)Al_(Y)As, a clad layer 48 made of n-type Ga_(1−X)Al_(X)As, a caplayer 49 made of n-type GaAs and an n-type electrode 50.

The semiconductor chip 41 emits a laser beam in a generally oval pattern51 as shown in FIG. 34. While according to the prior art the generallyoval pattern 51 of the laser beam is shaped into a round pattern for usein detection of the bar code, the present invention is such that, asshown in FIG. 35, the fluorescent ink deposit 18 forming each code barprinted on the fluorescent mark carrier is caused to assume a positionwith its lengthwise direction aligned with the major axis of thegenerally oval pattern of the laser beam at the time the fluorescentmark is irradiated. By so doing, the area of surface of the fluorescentink deposit 18 onto which the laser beam is projected increased ascompared with that exhibited by the use of the round pattern of thelaser beam and, consequently, a relatively high output can be obtainedto suit for a high speed reading.

The postal matters 13 are successively transported past the readingstation beneath the optical reading apparatus by the transport means 62which may be in the form of an endless belt conveyor equipped with aguide. However, even though the guide is employed, the postal matter 13being transported may tilt an angle of about 20 degrees at maximum. FIG.36 illustrates a condition in which, when the postal matter 13 beingtransported tilts (an angle of tilt being about 7 degrees), thefluorescent ink deposit 16 of a generally elongated shape confronts theirradiation pattern 51. If the irradiation pattern 51 has a minor axis64 which is too large, the irradiation pattern 51 may encompass theneighboring fluorescent ink deposits 18 which would eventually bringabout an undesirable result. As a result of studies conducted by theinventors, if the ratio (major axis/minor axis) of the minor axis 64relative to the major axis 63 of the oval irradiation pattern 51 exceeds15, information would be read out from the neighboring fluorescent inkdeposits 18 in the event of tilt as hereinabove described and,therefore, it has been found that the ratio of the minor axis 64relative to the major axis 63 of the irradiation pattern 51 should berestricted to a value smaller than 15.

Optical Reading Apparatus: Embodiment 2

FIGS. 37 and 38 are diagrams illustrating a mirror and a secondpreferred embodiment of the optical reading apparatus utilizing suchmirror, respectively.

As best shown in FIG. 37, a highly reflecting, generally disc-shapedmirror 29 having a reflectivity of 50% or more has its peripheralportion formed with a slit 52 so as to extend radially thereof. As shownin FIG. 38, this disc-shaped mirror 29 is so positioned as to permit theexciting light 60 from the semiconductor laser 27 to pass therethroughto irradiate the fluorescent ink deposit 18 on the postal matter 13 and,in this arrangement, the slit 53 in the disc-shaped mirror 29 is sooriented as to permit the irradiating pattern projected onto the postalmatter to have its major axis aligned with the lengthwise direction ofthe bar code defined by the fluorescent ink deposit 18. By sopositioning, as is the case with the oval irradiating pattern discussedhereinbefore, the bar code can be irradiated by the exciting light overthe substantially entire length thereof, permitting a relatively largeoutput to be obtained.

Optical Reading Apparatus: Embodiment 3

FIGS. 39 and 40 are diagrams illustrating different examples of use ofthe infrared-excitable fluorescent substance. As shown in FIG. 39, threefluorescent ink deposits 18 a, 18 b and 18 c are formed at respectivelypredetermined positions on a security 55. Each of these fluorescent inkdeposits 18 a to 1 c contains a different fluorescent substances havingits own peculiar emission spectrum.

For each of the fluorescent ink deposits 18 a to 18 b, a semiconductorlaser 27 a, 27 b or 27 c capable of emitting an exciting light of adifferent wave-length and a light receiving photodiode 34 a, 34 b or 34c for sensing fluorescent light emitted from the associated fluorescentink deposit 18 a, 18 b or 18 c are paired and arranged.

The respective fluorescent substances contained in the fluorescent inkdeposits 18 a to 18 c may be suitably chosen from a group of thefluorescent substances of the present invention. For example, thefluorescent substance in the fluorescent ink deposit 18 a may beNd_(0.1)Yb_(0.8) POc₄ having the emission spectrum as shown in FIG. 13,the fluorescent substance in the fluorescent ink deposit 18 b may beYb_(0.1) Yb_(0.9) PO₄ having the emission spectrum as shown in FIG. 14and the fluorescent substance in the fluorescent ink deposit 18 c may beEr_(0.2)Y_(2.8)Fe_(1.5)Al_(3.5)O₁₂ having the emission spectrum as shownin FIG. 17.

Accordingly, where the different fluorescent substances discussed aboveare employed for the fluorescent ink deposits 18 a to 18 c, thephotodiodes 34 a to 34 c receives different fluorescent light emittedtherefrom so that authenticity of the security 55 can be determined.Should even one of the photodiodes 34 a to 34 c fails to receive theassociated fluorescent light, the security 55 may be determined forged.

While in the example shown in FIG. 39 the use has been made of thefluorescent substances having the different emission spectra, it ispossible to form the single fluorescent ink deposit 18 using a mixtureof the fluorescent substances having the different emission spectra asshown in the example of FIG. 40.

Where the single fluorescent ink deposit 18 is formed using the mixtureof the different fluorescent substances, the exciting light of thedifferent wavelengths emitted from the semiconductor lasers 27 a, 27 band 27 c is projected onto the single fluorescent ink deposit 18 tocause the latter to emit the fluorescent light of different wavelengthswhich is sensed by the associated photodiodes 34 a, 34 b and 34 c. Inany one of the examples shown in FIGS. 39 and 40, an optical filteroperable to pass the fluorescent light of the wavelength of interestdesired to be sensed by the associated photodiode, but to cut off thefluorescent light not desired to be sensed by such associated photodiodeis fitted to a light receiving window of the respective photodiode 34 a,34 b and 34 c.

Optical Reading Apparatus: Embodiment 4

The emission intensity exhibited by the fluorescent substance having therelatively long fall time td has been shown in FIG. 3(c). This kind ofthe fluorescent substance having the relatively long fall time td isparticularly suitably employed for detection of information by theutilization of a fluorescent afterglow.

FIG. 41 illustrates a timing chart showing the timing of emission of thelight emitting element when the information is desired to be detected bythe utilization of the fluorescent afterglow and also showing an outputcondition of the light receiving element.

As shown in FIG. 41(a), the light emitting element cyclically blinkshaving an ON period T1 and an OFF period T2 which are substantiallyequal in duration with each other, so that the fluorescent ink depositcan be intermittently irradiated by the pulsating exciting light.Reference character S1 used therein represents a single pulse ofexciting light emitted by the light emitting element.

When the fluorescent ink deposit is excited by the pulsating excitinglight from the light emitting element, the fluorescent substancecontained therein emits the fluorescent light of such a waveform asshown in FIG. 41(b) showing an increase of the output level of thefluorescent light from the fluorescent ink deposit that continues upuntil the irradiation is interrupted. Even after the irradiation hasbeen interrupted, the light receiving element senses a fluorescentafterglow emitted from the fluorescent ink deposit. Since the durationof the fluorescent afterglow decreases with passage of time, a referencevalue Vs is set up so that comparison of the intensity of thefluorescent afterglow with this reference value Vs can provide arectangular signal S3, as shown in FIG. 41(c), subsequent tointerruption of the irradiation from the light emitting element.Accordingly, by repeatedly energizing and deenergizing the lightemitting element at short intervals, the code information represented bythe pattern of the bar codes can be optically read out.

The detection by the utilization of the afterglow of the fluorescentlight is particularly effective to provide a compact and inexpensiveoptical reading apparatus since not only is the light emitting elementdeenergized during the information reading, but also the fluorescentlight can be advantageously detected with no need to use any expensiveoptical filter.

FIGS. 42 and 43 are diagrams used to explain the optical readingapparatus operable with the afterglow of the fluorescent light discussedabove. Referring now to FIG. 42, the optical reading apparatus comprisesan irradiating pulse frequency selector switch 70, a pulse oscillatorcircuit 71, a transistor 72, a laser drive current limiting resistor 73,a drive circuit 74 having an automatic power control (APC) capability, asemiconductor laser diode 75, a condensing lens 76, a light receivingcircuit 77, a laser output adjusting potentiometer 78 and a hold circuit79.

The operation of the optical reading apparatus of FIG. 42 will now bedescribed. Assuming that the irradiating pulse frequency selector switch70 is held in position to select an adequate irradiation pulsefrequency, the pulse oscillator circuit 71 formulates a train of pulsesof a frequency determined by the position of the selector switch 70 andoutput them as a clock (CLK) signal.

This clock signal is utilized to switch the transistor 72 on/off tocontrol the supply of a laser drive current lout, outputted from the APCdrive circuit 74, to the semiconductor laser diode 75. The laser drivecurrent lout is limited by the laser drive current limiting resistor 73to a value necessary to avoid any possible breakage of the transistor 72and the semiconductor laser diode 75.

The pulsating exciting light 60 emitted from the semiconductor laserdiode 75 is projected onto the fluorescent ink deposit 18 on thefluorescent mark carrier 10 through the condensing lens 76, and theresultant fluorescent light (fluorescent afterglow) 61 emitted from thefluorescent ink deposit 18 during the OFF period of the semiconductorlaser diode 75 is detected by the light receiving circuit 77.

In order to obtain the pulsating exciting light at predeterminedintervals from the semiconductor laser diode 75, monitor light of thesemiconductor laser diode 75 is detected by the APC drive circuit 74 toeffect a feedback control on the laser drive current lout.

Detection of the monitor light is accomplished by supplying a monitorcurrent lin from the semiconductor laser diode 75 to the hold circuit 79which operates to detect the peak value or sample the monitor currentlin during the ON period of the semiconductor laser diode 75 and thenholds such status during the OFF period of the semiconductor laser diode75, so that the exciting light from the semiconductor laser diode 75 canbe controlled to accomplish a smooth excitation of the fluorescentsubstance by irradiation from the semiconductor laser diode 75. It is tobe noted that the output from the semiconductor laser diode 75 necessaryto excite the fluorescent substance is pre-adjusted by the laser outputadjusting potentiometer 78.

FIG. 43 illustrates the structure of the semiconductor laser diode 75referred to above. As shown therein, the semiconductor laser diode 75comprises a semiconductor laser 80 for emitting the exciting light, anda monitor photodiode 81 for receiving the exciting light from thesemiconductor laser 80 to provide the monitor light referred to above.

If a light emitting diode (LED) is used for a source of the excitinglight and a transistor is used to provide a pulsating exciting light bymeans of an switching operation of such transistor, it would bedifficult to secure a sufficient emission intensity during the detectioneven though the exciting light is throttled by a condensing light,resulting in limitation of the optical path length for informationreading.

In contrast thereto, with the reading apparatus shown in FIGS. 42 and43, the use has been made of the semiconductor laser diode excellent inlight converging capability and directionality and, therefore, eventhough the optical path length of the reading apparatus increases, asufficient emission intensity can be secured during the detection.

Also, the use of the drive circuit having the APC function for thesemiconductor laser diode is effective to substantially eliminate orreduce the temperature dependent change of the exciting light, making itpossible to increase the reliability in information reading.

Moreover, the circuit arrangement in which the monitor current is heldduring the ON period of the semiconductor laser diode and thesemiconductor laser diode drive circuit is controlled on a feedbackscheme based on the value of the monitor current permits the APCfunction to be exercised regardless of change in pulse frequency andduty ratio to facilitate the smooth excitation of the fluorescentsubstance, making it possible to increase the reliability.

Optical Reading Apparatus: Embodiment 5

A fifth preferred embodiment of the optical reading apparatus of thepresent invention will now be described.

A generally oblong card 80 such as, for example, a monetary cardcomprises, as shown in FIG. 44, a rectangular base plate 81 in the formof, for example, a generally oblong white-color film of polyester, anovercoat 82 of any desired design formed by printing on an upper surfaceof the base 80 and having a controlled light reflectivity, and anundercoat 83 formed on an undersurface of the base 81 on one side of thebase 81 opposite to the overcoat 82. The undercoat 83 is a rewritablemagnetic layer formed by painting a magnetic paint on the undersurfaceof the base 81. The overcoat 82 has an outer surface printed with apatterned fluorescent mark 84 containing the fluorescent substance, withsecurity information substantially permanently recorded in the card 80.

The mark 84 is a fluorescent mark of a kind invisible under visible raysof light and capable of emitting a fluorescent light 86 of a wavelengthdifferent from the center wavelength of the infrared exciting light 86when irradiated by such exciting light 86 and are comprised of aplurality of elongated parallel fluorescent bars laid so as to extendperpendicular to the lengthwise sense of the card 80. With thefluorescent mark 84 formed on the card 80, security informationincluding, for example, a code descriptive of the issuer of the cardand/or an ID code of the card bearer is recorded in the card 80.

While as shown in FIG. 45(d) the generally well-known standard bar codecomprises an oblong label 87 having a data area 89 b on which aplurality of parallel code bars 88 are printed so as to be visibleagainst the background of the label 87, the bar code formed as thefluorescent mark 84 in the practice of the present invention issubstantially reverse to the standard bar code. More specifically, thebar code forming the fluorescent mark 84 is in the form of an oblonglabel having one surface deposited with the fluorescent substances in apattern reverse to that of the standard bar code shown in FIG. 45(d)and, therefore, having a data area 89 in which respective portionscorresponding in position to the code bars 88 are left blank so as toleave fluorescent stripes 90 each between the neighboring bars 88 withopposite fluorescent leaders 91 and 91 a defined on respective endportion of the label.

With this design, regardless of the direction in which the data area 89is scanned, the position of the data area 89 can be easily detectedsince the leader 91 of a width greater than any one of the bars 88 andfluorescent stripes 90 both forming the data area 89 is first scanned asubstantial length of time. Also, the contrast of the data area 89 overthe entire area thereof is made substantially uniform so as to avoid anypossible erroneous detection of the thickness of the first one of thebars, i.e., the bar 88 a.

The fluorescent substance used to form the fluorescent mark 84 may beany fluorescent substance or a compound containing as an optical activeelement one or a mixture of rare earth elements such as, for example,neodymium (Nd), ytterbium (Yb), europium (Eu), thulium (Tm),praseodymium (Pr) and dysprosium (Dy) with the optical active elementbeing a compound containing in its matrix such oxides of tungstate,molybdate or phosphate. However, so far as the fluorescent light 86capable of emitting an afterglow can be emitted when the exciting lightof any arbitrarily chosen wavelength is irradiated, the material may besuitably changed.

In the embodiment under discussion, a fluorescent paint containing thefluorescent substance such as Li(Nd_(0.9)Yb_(0.1))P₄O₁₂ is printed toform the fluorescent mark 84. The fluorescent mark 84 so formed has sucha property that when near infrared rays of light of about 800 nm inwavelength are irradiated as the exciting light, the infraredfluorescent light 86 having a peak value in the vicinity of 1,000 nm canbe emitted and that the persistency of the fluorescent light 86 untilthe intensity thereof decreases down to 10% of the maximum intensitysubsequent to interruption of the irradiation lasts for about 400 to 600μsec.

The optical reading apparatus according to this embodiment comprises, asshown in FIG. 46, a card transport 92, an illuminating unit 93 forirradiating the card 80 carried by the card transport 92, aphotoelectric converter unit 95 for converting a light signal 94,emitted from an irradiated position, into an electric signal, afluorescent mark detecting unit 96 for detecting from the convertedelectric signal a mark signal S4 corresponding to the position at whichthe mark 84 is formed, and a data processing unit 97 for determiningcontents of the data on the card 80 from the detected mark signal S4.

The card transport 92 includes spaced pairs of rollers 99 adapted to bedriven by a motor drive circuit 98 for transporting the card 80, whilethe latter is sandwiched in between the rollers 99 of the pairs, at aspeed of, for example, about 200 to 400 mm per second with thefluorescent mark 84 on the card consequently moved beneath theilluminating unit 93 and the photoelectric converter unit 95. Dataassociated with the operating timing of the motor drive circuit 98 arefed back to the data processing unit 97 to acknowledge the timing atwhich a requisite data processing may take place to determine thecontents of the mark 84.

The illuminating unit 93 includes a illuminator drive power source 100for outputting a predetermined direct current voltage in synchronismwith the timing of detection of the mark 84 and a light source 101 whichis energized by the direct current voltage supplied from the powersource 100 to emit rays of light 85.

The light source 101 comprises a light emitting element 102 such as alight emitting diode capable of emitting near infrared rays of lighthaving an emission center wavelength in the vicinity of 800 nm, and alight guide 103 made of a glass fiber and fitted to a light exit of thelight emitting element 102 as shown in FIG. 44. This light source 101 isso positioned that a free end of the light guide 103 is spaced a minutedistance of about 2 mm or smaller from the surface of the card 80 andthe light guide 103 itself is tilted a predetermined angle θ1 within therange of 40 to 60° in a plane perpendicular to the direction of movementof the mark 84 relative to the horizontal direction.

The photoelectric converter unit 95 for converting the light 94 from theirradiated position on the card 80 into the electric signal includes adetector 104 for converting the incident light into an electric current,and an alternating current amplifier 105 for converting the current intoa voltage and then amplifying the converted voltage.

The detector 104 includes a light receiving element 106 such as aphotocell or a photodiode having a light receiving sensitivity to theinfrared region of light, an optical filter 107 fitted to a lightreceiving face of the light receiving element 106 for selectivelypassing only the wavelength of the fluorescent light 86 emitted from themark 84, and a light guide 108 similar to the light guide 103 used onthe light source 101 and secured thereto through the optical filter 107.

The light guide 108 of the detector 104 has its free end positioned inthe vicinity of the free end of the light guide 103 and is inclined atan angle θ2 within the range of, for example, about 105 to 115° in aplane perpendicular to the direction of movement of the mark 84 relativeto the horizontal direction. By so positioning the light guide 108, raysof light 94 including a reflected light component 109 reflected from theposition at which the mark 84 is irradiated by the exciting light 85 anda fluorescent light component 86 are received by the detector 104through the light guide 108 as incident light. The incident light 94 isconverted by the light receiving element 106 into the voltageproportional to the intensity of the incident light as shown in FIG.47(b), which voltage is then amplified by the alternating currentamplifier 105 to a predetermined voltage. The alternating currentamplifier 105 then outputs the signal S5 indicative of the amplifiedvoltage to the mark detecting unit 96 by which a signal corresponding tothe position of the mark can be detected.

The mark detecting unit 96 comprises a comparator 110 for outputting amark signal S4 of a waveform as shown in FIG. 47(c) and corresponding tothe position at which the mark is formed, a reference value settingcircuit 111 for setting a reference value Vc used by the comparator 110,and a data area determining circuit 112 for determining the data area 89in the mark 84. The reference value setting circuit 111 is operable todetect a portion of the electric signal S5 fed from the photoelectricconverter unit 95 which corresponds to the leader 91 of the mark 84 todetermine the reference value Vc proportional to the level of the leader91, which reference value Vc is subsequently inputted to the comparator110. Simultaneously therewith, the reference value setting circuit 11supplies a predetermined signal S6 to the data area determining circuit112 to acknowledge the latter that detection of the data area 89 hasbeen initiated.

The data area determining circuit 112 is used to acknowledge thecomparator 110 of the timing at which the input signal S5 is comparedwith the reference value Vc and operates to initiate detection of thestart of scan of the data area 89 in response to a start signal S6 fedfrom the reference value setting circuit 111 and also to detect the endof the data area 89 in response to the signal S4 outputted from thecomparator 110, thereby providing an output signal S7 with thecomparator 110. The comparator 110 provides an output signal S4 of asubstantially rectangular waveform as shown in FIG. 47(c) when the levelof the signal S5 fed from the photoelectric converter unit 95 decreasesdown to a value lower than the reference value Vc,which output signal S4is then supplied to the data processor 97 by which the pulse width andinterval of the signal S4 are measured to analyze the contents of thedata area 89 of the mark 84.

The operation of the mark detecting unit 96 will now be described withreference to the flowchart of FIG. 48. Assuming that the mark detectingunit 96 is brought into operation at step 120, initialization takesplace at step 121, followed by a reference value setting block.

In the reference value setting block, the timing at which the signallevel abruptly rises is constantly monitored at step 122 bydifferentiating the input signal S5 fed from the photoelectric converterunit 95. If the raise of the signal level is detected at a timing t1shown in FIG. 47, the program flow goes to step 123 at which a timer isstarted and at the subsequent step 124 a wait is made until the fall ofthe input signal is detected.

Once the fall of the signal level is recognized, the count of the timerindicative of the length of time passed is examined at step 125. Shouldthe decision at step 125 indicate that the length of time passes isshorter than a predetermined value, the input signal is deemed as anunnecessary signal such as, for example, a noise signal and the programflow goes back to step 122. However, if the decision at step 125.indicates that the predetermined length of time has passed at the timethe signal level detected at a timing t2 falls, the voltagecorresponding to the average voltage Vm of the signal level during aperiod between the rise and fall thereof which is divided by apredetermined rate is compared with the reference value Vc at step 126and is then inputted to the comparator 110. Simultaneously therewith,and at step 127, a signal S7 is supplied through the data areadetermining circuit 112 to the comparator 110 to cause the latter toinitiate a comparing operation.

During the comparison taking place at step 128, the comparator 110outputs a high-level signal during a period in which the level of theinput signal S5 falls below the reference value Vc and a low-levelsignal during a period in which it rises above the reference value Vc,to thereby output the mark signal S4 of the generally rectangularwaveform in correspondence to positions where no fluorescent deposit isformed.

Then, at step 129, a length of time during which the mark signal S4 isin the low level state is detected. If the length of time during whichthe mark signal S4 is in the low level state exceeds a predeterminedtime, the comparator 110 is acknowledged that the data area 89 of themark 84 has passed the reading station and the leader 91 a is alignedwith the reading station, with the comparing step consequentlyterminated.

It is to be noted that, in place of the use of the fluorescent markwhich corresponds to the reversal of the prior art code mark shown inFIG. 45(a), the fluorescent mark in which the reversed data area 89 maybe sandwiched between leaders 91 and 91 a as shown in FIG. 45(b) orfront and rear portions of the data area 89 a which are not reversed maybe sandwiched by leaders 91 and 91 a as shown in FIG. 45(c). If thedirection of scan of the fluorescent mark 84 is fixed in one direction,the use of only the leader 91 is sufficient and in such case the leader91 should be positioned at a location from which the scanning starts.Also, the leader 91 may not be always of a rectangular shape, but may beof any desired shape provided that a distinction can readily beaccomplished between it and the data area 89.

While the mark detecting unit 96 has been described as operable tosuccessively process the signal S5 fed from the photoelectric converterunit 95, the mark detecting unit 96 may be designed to sample and storea change in a series of input waveforms and then to detect the positionat which the mark 94 is formed by the utilization of such data by meansof the above described procedure or a similar procedure.

Moreover, instead of the detection of the fluorescent light 86 bycontinuously irradiating by the exciting light 85, the method ofdetecting the fluorescent light 86 can also be used to detect theposition at which the mark 84 is formed by intermittently irradiating bythe exciting light 85 and then by detecting the afterglow of thefluorescent light 86.

Yet, in place of the mark 84 being moved while the optical readingapparatus is fixed in position, arrangement may be made that theilluminating unit 93 and the photoelectric converter unit 95 may beintegrated together to provide a portable probe and in such case theoptical reading apparatus may be made movable manually or automaticallywhile the mark 84 is fixed in position. In addition, arrangement mayalso be made that, while the exciting light 85 is scanned at apredetermined angle, light emerging from the scanning position isdetected by the detector 104. These variants may equally apply to theremaining embodiments of the optical reading apparatus of the presentinvention.

Optical Reading Apparatus: Embodiment 6

A sixth preferred embodiment of the optical reading apparatus will nowbe described. The card 80 and the mark 84 used in connection with thisembodiment of the optical reading apparatus are similar to those used inconnection with the previously described fifth embodiment and,therefore, the details thereof are not herein reiterated.

The optical reading apparatus according to this embodiment comprises, asshown schematically shown in FIG. 49, an irradiating means 151 forintermittently irradiating the mark 84 by the exciting light 85 of apredetermined intensity at a predetermined cycle, a photoelectricconverting means 153 for receiving the incident light 94 emerging fromthe position where the exciting light 85 is projected and converting theincident light 94 into an electric signal, a waveform detecting means154 operable in synchronism with the timing of irradiation by theexciting light 85 from the irradiating means 151 to separately detect aminimum value shortly before the start of irradiation, a maximum valueshortly before interruption of the irradiation and a detected value 157immediately after interruption of the irradiation, and a markdetermining means 155 for comparing the detected value 157 with areference value 158 obtained by dividing the difference between themaximum and minimum values to determine the position at which the mark84 is formed in the event that the detected value 157 exceeds thereference value 158.

The photoelectric converting means 153 has an input side coupled with anoptical filtering means 152 for selectively passing only a lightcomponent of a wavelength included in the incident light 94, butmatching with that of the fluorescent light 86, and the waveformdetecting means 154 includes a signal input determining means 156operable to sample a value of the input waveform at a predeterminedtiming, retain such value for the subsequent sampling timing to come anddetermine whether or not the maximum value outputted from the detectingmeans 154 is significant. Only during a period in which the signal inputdetermining means 156 determines that the maximum value is significant,the mark determining means 155 undergoes a comparing operation.

More specifically, the optical reading apparatus according to thisembodiment comprises, as shown in FIG. 50 showing the details thereof, acard transport 92, an illuminating unit 93, a photoelectric converter94, a fluorescent mark detecting unit 96, a data processor 97 and asignal generating unit 130 for generating various control signals.

The signal generating unit 130 is operable to generate at least a drivesignal S8 used in the illuminating unit 93 and three timing signals S9,S10 and S11 used in the mark detecting unit 96 and, for this purpose,includes a clock signal generator 131 for generating a clock signal S12and a control signal generator 132 for generating the various controlsignals based on the clock signal S12.

The clock signal generator 131 continuously generates the clock signalS12 in the form of a train of pulses at a predetermined interval of, forexample, about 100 μmsec as shown in FIG. 52(a). The control signalgenerator 132 formulates the drive signal S8 of a generally rectangularwaveform having its level varying at an interval of about 500 μsec asshown in FIG. 52(b) by varying the levels of the signal each time fivepulses of the clock signal S12 are inputted thereto. Also, the controlsignal generator 132 outputs a pulse signal in synchronism with, forexample, the fourth, sixth and ninth pulses of the clock signal S12subsequent to the rise of the drive signal S8, to thereby form thetiming signals S9 to S11 in synchronism with the drive signal S8 asshown in FIG. 52(c) to FIG. 52(e), respectively.

The mark detecting unit 96 includes a sample-hold circuit 133 formeasuring a change of the signal S13 from the photoelectric converterunit 95 as shown in FIG. 52(f), first to third comparators 134, 135 and136, and first and second display circuits 137 and 138.

The sample-hold circuit 133 includes three sampling circuits 142 a, 142b and 142 c of a substantially identical construction each including avoltage buffer circuit 139 in the form of an operational amplifier, acapacitor 140 connected with one input of the voltage buffer circuit 139for holding an input voltage and an analog switch 141 adapted to betriggered on in response to the associated timing signal S9, S10 or S11fed from the signal generating unit 130.

This sample-hold circuit 133 is operable to individually and cyclicallysample the voltage varying signal S13 correspondingto the intensity ofthe incident light 94 as shown in FIG. 52(f) and retain such detectedvalue until the subsequent sampling timing.

In this embodiment, the timing signal S9 shown in FIG. 52(c) is suppliedto the first sampling circuit 142 a (See FIG. 51) so that the maximumvalue Vm of the incident light 94 shown by a bold line in FIG. 52(e) isdetected by the voltage immediately before the interruption ofirradiation by the light 85. Also, the timing signal S10 shown in FIG.52(d) is supplied to the second sampling circuit 142 b so that theintensity of the afterglow is detected in the form of a voltage Vd shownby the broken line in FIG. 52(g) by the voltage immediately after theinterruption of irradiation.

Also, the timing signal S11 shown in FIG. 52(e) is supplied to the thirdsampling circuit 142 c so that the minimum value of the incident light94 shown by the slender line in FIG. 52(g) is detected by the voltage V1immediately before restart of irradiation by the light 85. In this way,change of the waveform of the incident light 94 is determined in theform of a change of the voltage so that the percentage of the intensityof the afterglow relative to the whole can be determined.

The first comparator 134 for determining the value of each detectedvalue is employed in the form of an operational amplifier having anegative input terminal to which the voltage Vd proportional to theafterglow and outputted from the second sampling circuit 142 b isinputted as the detected value. On the other hand, the differencebetween respective voltages outputted from the first and third samplingcircuits 142 a and 142 b is divided by a variable resistor 142 toprovide a voltage Vc which is inputted to the first comparator 134 as areference value Vc as shown by the single-dotted line in FIG. 52(g).Thus, should the first comparator 134 determines that the detected valueVd exceeds the reference value Vc, a predetermined signal S14 isoutputted from the first comparator 134 to the third comparator 136.

The second comparator 134 compares the maximum value Vx, outputted fromthe first sampling circuit 142 a, with a predetermined reference valueand outputs a predetermined signal S15 when the maximum value Vmdecreases down below the reference value. However, if the maximum valueVm exceeds the predetermined reference value, the second comparator 134ceases outputting the signal S15. This second comparator 134 isconnected parallel to the first comparator 134 and has an outputterminal connected with the third comparator 136 through aforward-biased diode 144 so that the signal S15 can be supplied to thethird comparator 136.

The third comparator 136 is in the form of an operational amplifierhaving a negative input terminal adapted to receive respective outputsfrom the first and second comparators 134 and 135 and is operable tocompare them with a predetermined reference value so that a switchingelement 145 in the form of a field effect transistor coupled with anoutput stage of the operational amplifier can be controlled. Whileduring a period in which both of the respective output voltages from thefirst and second comparators 134 and 135 are lower than thepredetermined reference value, a “1” signal descriptive of detection ofthe fluorescent mark 84 is outputted to the data processor 97, a signalS16 to be supplied to the data processor 97 will be rendered to be “0”,descriptive of non-detection of the fluorescent mark 84, in the eventthat a high level signal is outputted from either one of the first andsecond comparators 134 and 135.

Accordingly, during a period in which an output signal S14 from thefirst comparator 134 is instable because the intensity of the incidentlight 94 is low, a high level signal S15 is supplied from the secondcomparator 135 to the negative input terminal of the third comparator136, causing an output of the third comparator 136 to be forciblyrendered zero (“0”) to acknowledge the data processor 97 that nofluorescent mark 84 has been detected.

Conversely, in a condition in which the intensity of the incident light94 is of a value higher than a predetermined value and detection of thefluorescent mark 84 takes place normally, the second comparator 135outputs a low level signal wherefore the third comparator 136 isoperated in response to change in level of the output from the firstcomparator 134, that is, in response to detection of the fluorescentcomponent, so that as shown in FIG. 52(h) the presence or absence of thefluorescent mark can be determined.

The timing at which the determination is carried out by the thirdcomparator 136 is visually indicated by emission of light from a lightemitting diode 146 of the first display circuit 137 coupled with anoutput of the second comparator 135. Also, the timing at which thefluorescent mark 84 is detected is visually indicated by emission oflight from a light emitting diode 147 of the second display circuit 138coupled with an output of the third comparator 136.

A capacitor 140 and a resistor 146 both disposed on an input stage ofthe sample-hold circuit 133 and a capacitor 149 and a resistor 150 bothdisposed on an input stage of the third comparator 136 constitute arespective integrating circuit operable to avoid any possible erroneousoperation which would result from an abrupt increase of the input levelin response to input of noise pulses.

The cycle of the drive signal S8 employed in the illustrated embodimentis about 1 msec which is about twice the persisting time of thefluorescent afterglow of the fluorescent substance forming thefluorescent mark 84, but the cycle and the persisting time can besuitably changed.

Also, the respective timings at which sampling signals S9 to S11 may beset to be about the timing at which the exciting light 85 is pulsated,in which case separation between the fluorescent light 86 and thereflected light 109 can be accomplished accurately. In such case, it ispossible to detect the value of the fluorescent light 86 withoutdetecting the afterglow, but in reference to the voltage immediatelyafter the start of irradiation and immediately before interruption ofthe irradiation.

In addition, the analog operational amplifier used in the variouscomparators for comparing the detected values with the associatedreference values may be replaced with a digital comparator such as, forexample, a microprocessor. In such case, in place of or in addition tothe selective sampling of the voltage value at a characteristic portionof the input waveform, the entire waveform may be detected so that achange thereof can be digitally processed.

Optical Reading Apparatus: Embodiment 7

The card 80 and the mark 84 used in connection with this seventhembodiment of the optical reading apparatus are similar to those used inconnection with the previously described fifth embodiment and,therefore, the details thereof are not herein reiterated.

The seventh embodiment of the optical reading apparatus is shownschematically in FIG. 53 and comprises an irradiating means 160 forintermittently irradiating the mark 84 by the exciting light 85 of apredetermined intensity at a predetermined cycle, a photoelectricconverting means 162 for receiving the incident light 94 emerging fromthe position where the exciting light 85 is projected and converting theincident light 94 into an electric signal, a waveform shaping means 163for inverting and amplifying a half of an output signal from thephoto-electric converting means 162 in synchronism with the timing 90°displaced in phase from the irradiating period of the exciting light 85from the irradiating means 160, a low pass filtering means 164 forselectively extracting a direct current component from an output signalfrom the waveform shaping means 163, and a comparing means 165 forcomparing a detected voltage outputted from the low pass filtering means164 with a reference voltage and for providing a predetermined marksignal therefrom in the event that the detected voltage exceeds thereference voltage.

More specifically, as shown in FIG. 54, the optical reading apparatuscomprises a card transport 166 for transporting the card 80, anilluminating unit 167 for illuminating the marking 84 on the card 80, aphotoelectric converting unit 168 for converting rays of light 94,emerging from the position of the mark 84 irradiated by the excitinglight 85, into an electric signal, a fluorescent mark detecting unit 169for outputting, based on the converted electric signal, a mark signalS28 descriptive of the position at which the mark 84 is formed, and adata processor 170 for determining contents of the data on the card 80in reference to the detected mark signal S28.

The card transport 166 includes spaced pairs of rollers 172 adapted tobe driven by a motor drive circuit 171 for transporting the card 80,while the latter is sandwiched in between the rollers 172 of the pairs,at a speed of, for example, about 200 to 400 mm per second with thefluorescent mark 84 on the card consequently moved beneath theilluminating unit 167 and the photoelectric converter unit 168. Dataassociated with the operating timing of the motor drive circuit 171 arefed back to the data processor 170 to acknowledge the timing at which arequisite data processing may take place to determine the contents ofthe mark 84.

The illuminating unit 167 includes an oscillator 173 for generating aclock signal S20 of a waveform as shown in FIG. 56(a), a signalgenerator 174 for generating two different control signals S22 and S23and a drive signal S21 in synchronism with the timing of the clocksignal S20, an illuminator drive circuit 175 for amplifying the power ofthe drive signal S21, and a light source 176 which is energized by thedrive circuit 175 to emit the exciting light 85. The oscillator 173 isoperable to continuously generate the clock signal S20 in the form of atrain of pulses at intervals of, for example, 250 μsec as shown in FIG.56(a).

The signal generator 174 includes, as shown in FIG. 55, first and secondD-type flip-flops 177 and 178 each having a clock signal input terminal179 and 180 which is connected with an output terminal of the oscillator173. The first flip-flop 177 also has a data input terminal 181 and anon-inverting output terminal 183 which are respectively connected withan inverting output terminal 182 and a data input terminal 43 of thesecond flip-flop 178.

With this structure, each time two pulses of the clock signal S20 areapplied to the signal generator 174, the drive signal S21 of arectangular waveform having its output level inverted at intervals ofabout 500 μsec is outputted from the non-inverting output terminal 183of the first flip-flop 177. A first control signal S22 of a frequencyequal to that of the drive signal S21, but retarded 90° in phase fromthat of the drive signal S21 is outputted from a non-inverting outputterminal 184 of the second flip-flop 178, and a second control signalS23 of a frequency equal to that of the drive signal S21, but advanced90° in phase from that of the drive signal S21 is outputted from aninverting output terminal 182 of the second flip-flop 178.

The illuminator drive circuit 175 is comprised of a transistor switch185 adapted to be turned on in response to the drive signal S21 andincludes a Zener diode 186 connected between the emitter and base of thetransistor switch 185 for limiting the base voltage, said transistorswitch 185 having a collector connected in series with a light emittingelement 187.

The light source 176 comprises the light emitting element 187 such as alight emitting diode capable of emitting near infrared rays of lighthaving an emission center wavelength in the vicinity of 800 nm, and alight guide made of a glass fiber and fitted to a light exit of thelight emitting element 187. This light source 176 is so positioned thata free end of the light guide is spaced a minute distance of about 2 mmor smaller from the surface of the card 80 and the light guide itself istilted a predetermined angle within the range of 45 to 60° in a planeperpendicular to the direction of movement of the mark 84 relative tothe horizontal direction. (In this connection, see FIG. 44.)

The photoelectric converter unit 168 includes a detector 188 forconverting the incident light into an electric current, and analternating current amplifier 189 for converting the current into avoltage and then amplifying the converted voltage. The detector 188includes a light receiving element such as a photocell or a photodiodehaving a light receiving sensitivity to the infrared region of light, anoptical filter fitted to a light receiving face of the light receivingelement for selectively passing only the wavelength of the fluorescentlight emitted from the mark 84, and a light guide similar to the lightguide used on the light source 176 and secured thereto through theoptical filter.

The light guide of the detector 188 has its free end positioned in thevicinity of the free end of the light guide and is inclined at an anglewithin the range of, for example, about 105 to 115° in a planeperpendicular to the direction of movement of the mark 84 relative tothe horizontal direction. By so positioning the light guide, rays oflight 94 emerging from the position at which the exciting light 85 isprojected onto the mark 84 can be received. As the incident light 94includes a reflected light component 109 reflected from the position atwhich the mark 84 is irradiated by the exciting light 85, a fluorescentlight component 86 and external light 190 (See FIG. 53) pass through theoptical filter, only the reflected light 109 and the external light 190,that is, rays of light of a wavelength other than that of thefluorescent light component 86, are attenuated to a value as small aspossible, and the light receiving element converts the incident lightinto an electric current proportional to the intensity thereof.

Also, after having been amplified to the predetermined value by thealternating current amplifier 189, a detected signal S24 of a waveformshown in FIG. 56(e) is inputted to the fluorescent mark detecting unit169 so that a signal S28 descriptive of the position where the mark 84is formed can be outputted selectively.

The seventh embodiment of the optical reading apparatus is characterizedin the structure of the fluorescent mark detecting unit 169. As shown inFIGS. 54 and 55, the mark detecting unit 169 includes a synchronousrectifying circuit 191 for shaping the detected signal S24 into apredetermined signal S25 of a waveform as shown in FIG. 56(f) by theutilization of the first and second control signals S22 and S23, a lowpass filter 192 for removing an alternating current component from thesignal S25 to provide a signal S26 which varies in level in dependenceon detection of the fluorescent light 86, and a comparator 193 foroutputting a mark signal S28 when a significant signal S26 is inputtedthereto.

The synchronous rectifying circuit 191 includes, as shown in FIG. 55, adifferential amplifying circuit 195 utilizing an operational amplifier194 having two input terminals 196 and 197 connected parallel to eachother to receive the detected signal S24 and also connected in serieswith respective analog switches 198 and 199, which analog switches 198and 199 are in turn adapted to be controlled respectively by the controlsignals S22 and S23.

In other words, the analog switch 198 connected with a positive inputterminal 196 of the operational amplifier 194 is adapted to be turned onduring a period in which the first control signal S22 is in a high levelstate, while the analog switch 199 connected with a negative inputterminal 197 of the operational amplifier 194 is adapted to be turned onduring a period in which the second control signal S23 is in a highlevel state.

While the period during which the first control signal S22 is in thehigh level state corresponds to the period retarded 90° in phase fromthe irradiating period during which the exciting light 85 is emittedfrom the light emitting element, the period during which the secondcontrol signal S23 is in the high level state corresponds to the periodadvanced 90° in phase from the irradiating period. Accordingly, of thedetected signal S24 inputted to the synchronous rectifying circuit 191,a latter half period during which the exciting light is emitted and afirst half period during which emission of the exciting light isinterrupted are inputted to the positive input terminal 196 of theoperational amplifier 194 through the analog switch 198 while a latterhalf period during which the emission of the exciting light isinterrupted and a first half period during which the exciting light isemitted are inputted to the negative input terminal 197 of theoperational amplifier 194 through the analog switch 199. As a resultthereof, a signal S25 emerges from the synchronous rectifying circuit191 which signal S25 has a waveform shown in FIG. 56(f) which assumes aplus voltage during a period in which the detected signal S24 isinputted to the positive input terminal 196 and a negative voltageduring a period in which the detected signal S24 is inputted to thenegative input terminal 197.

In the meantime, since the change in voltage of the detected signal S24takes place in a pattern of a rectangular waveform as shown by thesingle-dotted line in FIG. 56(e) since only the reflected light 109comes from the mark 84 and the card 80 during the period in which theexciting light 85 is not projected onto the fluorescent mark 84.Accordingly, the output signal from the synchronous rectifying circuit191 is of such a waveform as shown by the hatched areas in FIG. 56(f) inwhich a first half of the reflected light component is inverted and alatter half thereof is not inverted and is in the form of a signalhaving plus and minus sides of an equal value.

On the other hand, when the exciting light 85 scans across thefluorescent mark 84, the fluorescent component increases exponentially,as shown by the solid line in FIG. 56(e), subsequent to the irradiationby the exciting light due to the persistency of the fluorescent light 86and also decreases exponentially subsequent to the interruption ofirradiation by the exciting light. Accordingly, the output signal S25from the synchronous rectifying circuit 191 is selectively non-invertedand amplified during the period in which the fluorescent component ishigh, or inverted and amplified during the period in which thefluorescent component is low, and consequently, a signal having a plusside sufficiently higher than the minus side can be drawn from thesynchronous rectifying circuit 191.

In view of this, in the illustrated embodiment, the output signal S25from the synchronous rectifying circuit 191 is allowed to pass throughthe low pass filter 192 so that an alternating current component can beremoved, leaving only a direct current component to be outputted fromthe low pass filter 192. In other words, as shown by the single-dottedchain line shown in FIGS. 56(e) and 56(f), no output emerge from the lowpass filter 192 when the fluorescent mark 84 is not scanned, because theplus side and the minus side are of a equal quantity.

However, as shown by the solid line in FIG. 56(e), when the mask 84 isscanned, the external light 190 and the reflected light 109 arecancelled, but the fluorescent light 94 has a plus side considerablyhigher than the minus side. Accordingly, the signal S26 in the form of apositive direct current voltage is outputted from the low pass filter192.

The signal S26 emerging from the filter 192 is in turn inputted to thecomparator 193 utilizing an operational amplifier 20 and is compared inthe comparator 193 with a reference voltage S27 which corresponds thevoltage, stabilized by a constant voltage diode 102, that is divided bya variable resistor 202. When the significant signal S26 exceeding thereference voltage S27 is inputted to the comparator 193, an outputvoltage thereof is rendered to be in a high level state and the marksignal S28 descriptive of the detection of the mark position can beoutputted from the comparator 193.

It is to be noted that in the illustrated embodiment the drive signalS21 has a cycle of about 1 msec which is about twice the persisting timeduring which the afterglow from the fluorescent substance forming thefluorescent mark 84 continues. However, it is pointed out that the cycleand the persisting time may be suitably varied.

Optical Reading Apparatus: Embodiment 8

Before the description of an eighth preferred embodiment of the opticalreading apparatus proceeds, an example of the fluorescent mark will bediscussed with reference to FIG. 57. As shown in FIG. 57, a fluorescentmark 210 in the form of a bar code is formed on a carrier 211 such as,for example, a card, by the use of a printing technique and covered by aprotective sheet 213 bonded to the carrier 211 by means of a bond layer212.

The fluorescent mark 210 is prepared by the use of a transparent inkingmedium containing fluorescent microparticles capable of being excited byirradiation of, for example, infrared rays of light, whichmicroparticles are dispersed and retained in a binder. The fluorescentmicroparticles may be microparticles of an organic compound such as, forexample, Rhodamine 6G, Thioflavine or Eosine or of an inorganic compoundsuch as NdP₅O₁₄, LiNdP₄O₁₂ or Al₃Nd(BO₃)₄.

The binder used may be one or a mixture of, for example, wax, polyvinylchloride-vinyl acetate copolymer, ethylene-vinyl acetate copolymer,polyester, polyurethane and carbonate. If desired, a suitable quantityof one or both of a plasticizer and a surface active agent may beemployed.

As a printing method, any printing method may be employed such as, forexample, a thermal transfer technique in which an ink ribbon comprisinga ribbon base having one surface coated with the transparent inkingmedium is mounted on a thermal head so that the inking medium can bethermally transferred onto a surface of the merchandise as the carrieror a screen printing technique in which the transparent inking medium ina liquid form is printed onto the surface of the merchandise. Thesuitable printing method may be selected depending on the type and shapeof the carrier.

The bond used to form the bond layer 212 may be a bonding agent of anon-solvent type such as, for example, a hot-melt bonding agent, inorder to avoid any possible swelling, or deformation upon dissolution,of the fluorescent mark 210. The hot-melt bonding agent referred toabove may be of a kind containing an ethylene-vinyl acetate copolymer,polyethylene, polyamide or polyester.

The protective sheet 213 may be a transparent resinous sheet made of,for example, vinyl chloride or polyester. The carrier 211 of thefluorescent mark 210 may have a while-color layer formed thereon forenhancing the reflection of light and also enhancing the level of asignal detected from the fluorescent mark 210.

As shown therein, when infrared rays of light 214 of a center wavelengthmatching with that at which the fluorescent substance used can beexcited are projected onto the fluorescent mark 210, the fluorescentmicroparticles are excited in response to application of the infraredrays of light 214 to emit the fluorescent light 215 of a particularwavelength different from the center wavelength of the infrared rays oflight 214. If the fluorescent light 215 is received and converted intoan electric signal by a light receiving element and is subsequentlydigitized, a binary signal descriptive of the pattern of code barsforming the fluorescent mark 210 can be obtained so that informationrepresented by the fluorescent mark 210 can be read out.

FIG. 58 illustrates the optical reading apparatus according to theeighth embodiment. As shown therein, the optical reading apparatuscomprises a light emitting element 216, a light receiving element 217,an optical filter 218, an amplifier 219, a first amplification settingunit 220 for maximizing the amplification factor of the amplifier 219, asecond amplification setting unit 221 for setting the amplificationfactor to a medium value, a third amplification setting unit 222 forminimizing the amplification factor, a signal detector 223, and a clocksignal generator 224 for applying a drive clock to the signal detector223.

The signal detector 223 includes an analog-to-digital (A/D) converter225 for converting an analog reproduction signal a into a digitalsignal, a processor (CPU) 226 for analyzing a bar code signal from abinary signal outputted from the A/D converter 225, a memory device 227comprised of, for example, a program memory and a work memory, and aninterface (I/O) port 228 for controlling inputs and outputs.

The I/O port 228 outputs a signal necessary to select one of the firstto third amplification setting units 220, 221 and 22 based oninstructions from the processor 226 which determines a favorableamplification factor in reference to the status of the analogreproduction signal a received by the A/D converter 225. The signaldetector 223 is operable to reproduce the bar code signal from theanalog reproduction signal a based on a program stored in the memorydevice 227 and then output the bar code through the I/O port 228.

The optical reading apparatus 229 of the above described structure is,as shown in FIG. 59, disposed so as to confront the path 230 of movementof the carrier 211. On one side of the path 230 of travel of the carrier221 opposite to the side where the light emitting element 216 and thelight receiving element 217 both mounted on the optical readingapparatus 229 are disposed, a reflector 231 is disposed so as to reflectthe infrared rays of light from the light emitting element 216 backtowards the light receiving element 217 across the path 230 of travel ofthe carrier. In this arrangement, the light receiving element 217 isadjusted to generate an output signal of a saturation level so long asthe entire quantity of the infrared rays of light are reflected theretoby the reflector 231.

The sequence of reading the fluorescent mark performed by this opticalreading apparatus will now be described with reference to FIGS. 60 to62.

Assuming that the apparatus is electrically powered, the firstamplification setting unit 220 is selected according to instructionsissued from the processor 226 at step 240 to determine the initialamplification factor of the amplifier 219. At step 241, a wait is madeuntil the carrier 211 is moved past the reading station.

Although during this wait the infrared rays of light is projected fromthe light emitting element 216, and so long as no carrier 211 is presentat the reading station between both of the light emitting and receivingelements 216 and 217 and the reflector 231, the infrared rays of lightprojected by the light emitting element 216 are reflected by thereflector 231 so as to be incident upon the light receiving element 217and, therefore, as shown by an area A in FIG. 61(a), the analogreproduction signal a attains the saturation level Vref.

However, as the carrier 211 moves past the reading station between bothof the light emitting and receiving elements 216 and 217 and thereflector 231, the infrared rays of light from the light emittingelement 216 first impinge upon a non-mark area of the carrier 211 whereno fluorescent mark 210 is printed and are then reflected therebytowards the light receiving element 217. In general, since thereflectance of the carrier 211 is lower than that of the reflector 231,the level of the analog reproduction signal a decreases as shown by anarea B in FIG. 61(a).

At this time, the processor 226 determines at step 242 the level of theanalog reproduction signal a. In the event that it is determined thatthe level of the analog reproduction signal a resulting from irradiationof the non-mark area of the carrier 211 is higher than a gaindetermination level at which the gain is changed (corresponding tocarrier areas (a) and (b) shown in FIG. 61(a)), the second amplificationsetting unit 221 is selected according to instructions given by theprocessor 226 with the amplification factor of the amplifier 219consequently lowered to an intermediate value at step 243. Thus, thelevel of the analog reproduction signal a attributable to the carrierareas (a) and (b) is lowered down to a value lower than the determininglevel Vth as shown by the broken line in FIG. 61(a).

In the event that the level of the analog reproduction signal aattributable to the non-mark area of the carrier is determined lowerthan the determining level Vth (corresponding to the carrier areas (c)and (d) shown in FIG. 61) at step 242, and after the amplificationfactor of the amplifier 219 at step 243 has been lowered, the programflow goes to step 244 at which a wait is made until the fluorescent mark210 would be brought to the reading station. When while the infraredrays of light are continuously projected from the light emitting elementtowards the reading station the fluorescent mark 210 carried by thecarrier 211 arrives at the reading station, the fluorescent substancescontained in the fluorescent mark 210 is excited to emit a fluorescentlight and, therefore, the level of the analog reproduction signal aincreases.

At this time, the processor 226 executes step 245 to determine the levelof the analog reproduction signal a. In the event that the peak value ofthe analog reproduction signal a attributable to the bar code area ofthe fluorescent mark 210 is determined higher than the gaindetermination level Vth (corresponding to the carrier areas (a) and (b)as shown in FIG. 61(b)), the third amplification setting unit 222 isselected according to instructions from the processor 226. Accordingly,the peak value of the analog reproduction signal a attributable to thecarrier areas (a) and (b) is lowered to a value lower than the gaindetermination level Vth as shown by the broken line in FIG. 61(b).

In the event that the peak value of the analog reproduction signal aattributable to the bar code area is determined lower than the gaindetermination level Vth at step 245 (corresponding to the carrier areas(c) and (d) shown in FIG. 61(a)), and after the amplification factor ofthe amplifier 219 has been lowered at step 246, the program flow goes tostep 247 at which the fluorescent mark 210 is digitized to the last codebar thereof.

FIG. 62 illustrates the waveform of an output from the light receivingelement 217, that of the analog reproduction signal outputted from theamplifier 219 and that of the binary signal outputted from the signaldetector 223. FIG. 62(a) is a diagram showing the waveform of the outputfrom the light receiving element 217, FIG. 62(c) is a diagram showingthe waveform of the binary signal outputted from the signal detector223, and FIG. 62(b) is a diagram showing the waveform of the analogreproduction signal outputted from the amplifier 219 when the firstamplification setting unit 220 has been selected. FIG. 62(b′) is adiagram showing the waveform of the analog reproduction signal outputtedfrom the amplifier 219 when the second amplification setting unit 221has been selected, and FIG. 62(b″) is a diagram showing the waveform ofthe analog reproduction signal from the amplifier 219 when the thirdamplification setting unit 222 has been selected.

As can be seen from FIGS. 62(a) to 62(b″), if the amplification factorof the amplifier 219 is suitably changed depending on the level and theamplitude of the analog reproduction signal to thereby adjust the leveland the amplitude of the analog reproduction signal to a predeterminedvalue, the binary signal can be obtained by slicing the analogreproduction signal with a slice signal VT of a predetermined particularlevel.

Since the optical reading apparatus according to the eighth embodimentis so designed that the amplification factor of the amplifier 219 can bechanged to one of three factors depending on the level and the amplitudeof the analog reproduction signal a to thereby make the analogreproduction signal a match with the slice signal VT of thepredetermined particular level at all times, there is no possibilitythat the signal reading from the mark would become inaccurate and/orimpossible due to the difference in physical property of the carrier 211and, therefore, the apparatus is excellent in versatility andreliability. Also, since the binary signal can be obtained by slicingthe analog reproduction signal a with the single slice signal VT, thesignal detector 223 can be made simple in structure.

Although in this embodiment the amplification factor of the amplifier219 has been described as changed to one of the three factors dependingon the level and amplitude of the analog reproduction signal a, thereflected light component from the carrier 211 and the fluorescent lightcomponent from the mark 210, it may be made to be changed to one of twoor four or more factors. In addition, if an electronic potentiometer isemployed for the amplification factor setting unit, a continuous changeof the amplification factor of the amplifier 219 will be accomplished.

Optical Reading Apparatus: Embodiment 9

In the eighth embodiment described above, the reflector 231 has beendisposed in face-to-face relation with both of the light emittingelement 216 and the light receiving element 217. However, as shown inFIG. 63, in place of the use of the reflector 231, a light absorbentelement 249 capable of absorbing the rays of light projected from thelight emitting element 216 may be employed and disposed at the positionconfronting both of the light emitting and receiving elements 216 and217 across the path 230 of travel of the carrier 211.

In the embodiment shown in FIG. 63, during a wait being made until thecarrier 211 is moved past the reading station, the infrared rays oflight projected from the light emitting element 216 are absorbed by thelight absorbent element 249 with no light substantially impinging uponthe light receiving element 217 and, therefore, as shown by an area A inFIG. 64(a), the analog reproduction signal a is substantially at aground level AGND.

However, when the carrier 221 is brought to the reading station betweenthe light emitting element 216 and the light absorbent element 249, aportion of the infrared rays of light from the light emitting element216 is reflected by the carrier 211 so as to impinge upon the lightreceiving element 217 and, therefore, the analog reproduction signal aincreases as shown by an area B in FIG. 64(a). When the mark 210 issubsequently brought in register with the reading station and isconsequently irradiated by the infrared rays of light, the fluorescentlight emitted from the fluorescent substance forming the mark 210 isreceived by the light receiving element 217 as well and, therefore, theanalog reproduction signal a further increases as shown by an area C inFIG. 64(a). Accordingly, by determining if the level of the analogreproduction signal in the area B has exceeded the gain determinationlevel Vth for the selection of the amplification factor and by loweringthe amplification factor of the amplifier 219 in the event that it hasexceeded such gain determination level Vth, the signal reproduction canbe accomplished in a manner similar to that according to the previouslydiscussed eighth embodiment.

Optical Reading Apparatus: Embodiment 10

The details of the amplifier and the signal detector used in the tenthpreferred embodiment of the optical reading apparatus are shown in FIG.65. As shown therein, the optical reading apparatus comprises a firstdifferential amplifier 251 including a first operational amplifier 25and first to third resistors R1, R2 and R3; a second differentialamplifier 253 including a second operational amplifier 252 and fourth tosixth resistors R4, R5 and R6; a first comparator 254 connected with thefirst operational amplifier 251; a first variable resistor VR1 forsetting a slice level for the first comparator 254; a second comparator255 connected with the second operational amplifier 253; a secondvariable resistor VR2 for setting a slice level for the secondcomparator 255; a one-shot multivibrator 256 adapted to be triggered byan output signal f from the first comparator 254 to generate a pulse ofa predetermined pulse width each time it is triggered; an inverter 257for inverting an output signal from the one-shot multivibrator 256; anAND gate 258 for providing a logical product of respective outputsignals g and h from the second comparator 255 and the inverter 257; andan OR gate for providing a logical sum of respective output signals iand f from the AND gate 258 and the first comparator 254.

According to the tenth embodiment, the amplification factor of the firstdifferential amplifier 251 and that of the second differential amplifier253 are adjusted to be low and high, respectively, and the slice levelof the first comparator 254 is equalized to that of the secondcomparator 255. The pulse width of the pulse outputted from the one-shotmultivibrator 256 is adjusted to a value equal to the length of timerequired for the irradiating light to scan the narrowest stripe betweenthe neighboring code bars forming the fluorescent mark (bar code).

The operation of the optical reading apparatus will now be described.

FIG. 66 illustrates the waveform of a first analog reproduction signala1 outputted from the first differential amplifier 251. Referencecharacter A in FIG. 66 represents the signal obtained when the level ofthe light reflected from a surface of the carrier is low and the levelof the fluorescent light from the mark is high; reference character Brepresents the signal obtained when the level of both of the lightreflected from the carrier and the fluorescent light from the mark islow; and reference character C represents the signal obtained when thelevel of the reflected light from the carrier and that of thefluorescent light from the mark are high and low, respectively. Whenthis first analog reproduction signal al is digitized by the firstcomparator 254, such a binary signal f as shown in FIG. 68(a) can beobtained.

FIG. 67 illustrates the waveform of a second analog reproduction signala2 outputted from the second differential amplifier 253. Referencecharacters A′, B′ and C′ used in FIG. 67 corresponds respectively to A,B and C shown in FIG. 66. Thus, when the second analog reproductionsignal a2 is similarly digitized by the second comparator 255, such abinary signal g as shown in FIG. 68(b) can be obtained.

The output signal h from the inverter 257 is such as shown in FIG. 68(c)since the pulse width of the pulse outputted from the one-shotmultivibrator 256 is chosen to be equal to the length of time requiredfor the exciting light to scan the narrowest stripe between theneighboring code bars forming the fluorescent mark (bar code).Accordingly, the logical product of the output signals g and hrespectively from the second comparator 255 and the inverter 257 whichis obtained from the AND gate 258 is represented by an output signal ifrom the AND gate 258, the waveform of which is shown in FIG. 68(d).Also, the logical sum of the output signals i and f respectively fromthe AND gate 258 and the first comparator 254 which is obtained from theOR gate 259 is represented by an output signal j from the OR gate 259,the waveform of which is shown in FIG. 68(e), and, accordingly, a barcode signal can be detected.

According to the tenth embodiment, the binary signal corresponding tothe whole analog reproduction signals is obtained by preparingseparately the first binary signal f corresponding to the detectedsignal of a high level and the second binary signal g corresponding tothe detected signal of a low level and then providing the logicalproduct and sum of those signals. Accordingly, even though the detectedsignal descriptive of a series of marks formed on the single carriervaries partly in level, an accurate information reading is possible.

While in the embodiment described above, the two comparators 254 and 255have been described as having an equal slice level, the slice level ofone of the comparators 254 and 255 may differ from that of the other ofthe comparators 254 and 255.

Optical Reading Apparatus: Embodiment 11

An eleventh embodiment differs from the optical reading apparatus ofFIG. 65 in that the two differential amplifiers 251 and 253 have anequal amplification factor and the two comparators 254 and 255 haveslice levels different from each other.

As shown in FIG. 69, the analog reproduction signals a outputtedrespectively from the first and second differential amplifiers 251 and252 are of an equal level and are sliced respectively by the first slicesignal S1, set in the first comparator 254, and the second slice signalS2 set in the second comparator 255.

The first slice signal S1 slices high level portions A and C of theanalog reproduction signal a to provide a binary signal f correspondingto that shown in FIG. 6(a). On the other hand, the second slice signalS2 slices a low level portion of the analog reproduction signal a toprovide a binary signal g corresponding to that shown in FIG. 68(d).Accordingly, when the logical sum of the output signals f and grespectively from the first comparator 254 and the second comparator 255is obtained from the OR gate 258, the output signal j shown in FIG.68(e) can be obtained and, therefore, the mark information can beassured read from the detected signal then varying partly in level.

It is to be noted that although in each of the tenth and eleventhembodiments reference has been made to the use of the two differentialamplifiers and the two comparators, the number of each of thedifferential amplifiers and the comparators may further be increased.The greater the number of each of the differential amplifiers and thecomparators, an accurate information reading is possible from thedetected signal or the analog reproduction signal which is morecomplicated.

Industrial Applicability

The optical reading system of the present invention is applicable in thefollowing applications and has the following features.

a) Factory Automation

During automobile assemblage, car management, that is, classification ofcars according to the brand, export destination, date of manufactureand/or product lot number, can be accomplished using a fluorescent markwithout adversely affecting the appearance of each car.

b) Even if the fluorescent marking is printed on a black-color item suchas tires or on a transparent item of glass or synthetic resin, which hashitherto been unable to read with the prior art reflective bar code, themark can be assured read out.

c) Since even if any ornamental design is printed over the fluorescentmark, such fluorescent mark can readily be read out, a plurality ofpieces of information can be overlapped one above the other and,therefore, a limited space such as found in a price tag or a product tagof the merchandise can be effectively utilized.

d) By a reason similar to (a) and (b) above, effective utilization ispossible to products such as cosmetics and medicines, the design ofwhich is considered of importance, or to boxes or packages which arerequired for a high quality sensation to be appealing.

e) Even under the environment in which the prior art reflective bar codecannot be used due to the presence of oil and dust such as found in afactory or plant, the fluorescent mark can assuredly be read out.

f) By a reason similar to (a) and (b) above, for the convenience on thepart of a manufacturer, a concealed code may be provided on invoicesissued to clients for management purpose. (In general, the invoices arespecified by clients or of a format in which a client writes down.)

g) Information may be provided on a card-like item as a concealed codeso that the card-like item can be used as a game card (bar code game).

h) By a reason similar to (a) and (c), if used in connection withmanagement of books, literature or drawings, the design will not beadversely affected.

i) Not only can any possible forgery of a student's certificate or an IDcard be prevented, but also the certificate or ID card can be reduced insize or space.

k) Not only can any possible forgery of a stamp card or a point card beprevented, but also the card can be reduced in size or space.

l) Any possible forgery can be prevented by introducing the system ofthe invention in a Pachinko gift-exchange system.

What is claimed is:
 1. A mark to be detected containing a fluorescentsubstance capable of emitting light of a wavelength different from thatof an exciting light, comprising: a data area formed with a patterncorresponding to data to be recorded; and a lead-in area formed at asite that is scanned prior to irradiation with the exciting light uponthe data area, said lead-in area continuing a sufficient length greaterthan the longest continuous portion of the pattern formed at the dataarea, and said lead-in area that is formed at said site containing afluorescent substance.
 2. The mark to be detected as defined in claim 1,characterized in that the pattern formed on the data area is a patternof bar codes; in that the data area formed by a plurality of bars and abackground of the data area where the bars are arranged are formed on amedium as inverted by the fluorescent substance such that the lead-inarea is formed so as to encircle a predetermined width around the dataarea.
 3. A method for detecting a mark of a kind defined in claim 1 or2, which comprises: a light irradiating step of projecting light of asubstantially constant intensity; an photoelectrically converting stepof receiving the light emitted from a light emitting position andconverting it into an electric signal; a comparison value setting stepof automatically setting a comparison value from an electric signalcorresponding to the lead-in area of the mark; and a mark determiningstep of comparing a detected value corresponding to the data area in themark with the comparison value and determining, in the event that thedetected value exceeds the comparison value, the position at which themark is formed.
 4. A method of detecting a mark by irradiating the mark,containing the fluorescent substance, with an exciting light andreceiving a fluorescent light emitted from the mark, which methodcomprises the steps of: a step of intermittently projecting the excitinglight of a substantially constant intensity; a step of receiving light,emitted from an irradiating position of the exciting light andconverting it into an electric signal; an incident light intensitydetecting step of outputting as a comparison value an electric signalcorresponding to the intensity of incident light during an irradiatingperiod; a fluorescent intensity detecting step of outputting, as adetected value, an electric signal indicative of the magnitude of afluorescent component of the incident light; and a determining step ofcomparing the detected value with a comparison value and determining, inthe event that the detected value exceeds the comparison value, theposition at which the mark is formed.
 5. The mark detecting method asdefined in claim 4, wherein the incident light intensity detecting stepincludes a step of detecting the intensity of the incident lightimmediately after start of the irradiation and a step of detecting theintensity of the incident light shortly before interruption of theirradiation, said comparison value being obtained by dividing thedifference between those intensities.
 6. The mark detecting method asdefined in claim 4, wherein during the fluorescent intensity detectingstep, the intensity of the incident light immediately after interruptionof the irradiation is detected to provide the detected value.
 7. Themark detecting method as defined in claim 4, wherein the fluorescentintensity detecting step includes a step of detecting the intensity ofthe incident light immediately after start of the irradiation and a stepof detecting the intensity of the incident light shortly beforeinterruption of the irradiation, the detected value being formed byobtaining the difference between those intensities.